I know I'm too stupid for this game, but...

[Angelhearth]

Never done Leveling Roulette. Thought that was something for healers, as the few times I checked that was the class in demand. As for dungeons, I'm not very good at it due to health related issues (which I was soundly ridiculed for last time I mentioned it), so I tend to do things solo, as much as possible. I did the first dungeon (Holmister?), took me 1 try before I got it. Wanted to try it with my Red Mage, but it's at the early part of 70, and not eligible yet. SO I went back and tried doing some quests in the previous expansion, but getting 12 million or whatever it is with a reward of just over 100.000 isn't very funny. I haven't found any fates for lvl 70+, where are they (except for DoH and DoL).

[Edax]

Never done Leveling Roulette. Thought that was something for healers, as the few times I checked that was the class in demand. As for dungeons, I'm not very good at it due to health related issues (which I was soundly ridiculed for last time I mentioned it), so I tend to do things solo, as much as possible. I did the first dungeon (Holmister?), took me 1 try before I got it. Wanted to try it with my Red Mage, but it's at the early part of 70, and not eligible yet. SO I went back and tried doing some quests in the previous expansion, but getting 12 million or whatever it is with a reward of just over 100.000 isn't very funny. I haven't found any fates for lvl 70+, where are they (except for DoH and DoL).

The leveling roulette gives everyone a lot of exp when your finished with it, even if you get stuck fighting Ifrit again at level 20. The only downside is that the queue times for DPS are pretty poor.

[VictorTheed]

Those roullets that say healer in need will still give good exp for a tank or dps so don't sorry bout what role is in need.

Plus at were your at in game then can always run dungeons like holmistsr switch with your trust NPCs if you don't wanna do em with other players plus do fates in ahm areng of kholousia, those are other good solo says to lvl

[kaynide]

+1 to the roulettes. You have been missing out, friend! The side quests can be fun, but their rewards are pretty abysmal. You can expect to get about a level a day with leveling roulette + trials + some odds and ends. Faster if you are “in demand” (usually tank/healer, but sometimes dps too!)

[MariaArvana]

As others have said, queue up roulettes. They can be done on any job to give it large amounts of exp once per day, what you saw was the 'adventurer in need' bonus, which is just a little extra exp/gil added on to help incentivize people of certain roles to queue due to demand. In particular, Main Scenario roulette is a very easy roulette that rewards a lot of exp. Considering the majority of the dungeon run will be cutscenes and you vastly outgear the dungeon in question, there should be little stress on you even with any health issues you have that you mentioned in your 2nd post.

That being said, even if you funnel all quest exp into a single job, the SHB MSQ is designed to essentially level lock you multiple times throughout the run up to 80, you will have to queue up dungeons at some point or another if you want to reach 80 in a decent timeframe. That being said, if you're worried about dungeons, there is a system called trusts for shadowbringer dungeons- where you can play along with several NPC characters and effectively play solo at your own pace if you're worried about personal health issues disappointing other players.

Also, once you reach the end of the level 73 portion of the story, there'll be a sidequest chain that'll open up in the Crystarium in the bottom right corner of the map that'll unlock the ability to do daily quests - a set of three quests daily that give you 1+million exp each for finishing them, that are fully soloable, and can be done once a day. So if you're truly aversed to doing group content, you only really have to get up to the end of the 73 MSQ, then even if it'd be slow, you can use these daily quests to level your character whenever you reach level locks without having to do dungeons.

Finally, if you do all the sidequests, you won't really have to 'grind' dungeons, as most of the level locks are designed that even after you exhaust all the sidequests of that level range, you'll only really need to do the level appropriate dungeon 1-2x to reach the next level.

[Frizze]

I haven't found any fates for lvl 70+, where are they (except for DoH and DoL).

Kholusia, Ahm Araeng, and Lakeland. In the "starting area" for each of these zones there are level 70 and 71 fates. Trust runs are worth a few million exp each once you can do them. Clan hunts are good exp. And it might not hurt to unlock the first beast tribe when you can for their repeatable quests.

[MoonPhaseAlpha]

Run Holminster Switch with Trusts to 72. You can use Trusts to level up to 80. I would recommend focusing on one job to 80 though. When I got to Shadowbringers and hit the level requirement roadblocks, I ran the Shadowbringers dungeons to level up my BRD to 80, all with Trusts. I never ran any of those dungeons with others. And still haven't. I've leveled a WHM and AST 71-80 all with Trusts. Keep in mind, the Trusts don't earn experience/level during the MSQ while you're working your way through. They will reset to 71 after completing Shadowbringers. But they will automatically hit levels 73/75/77/79 so you can use them in the dungeons to level yourself up.

You can still do FATEs in Lakeland, Ahm Araeng and Kholusia in those starting areas at 70, just won't get as much as experience. The penalty isn't horrible. I think I was getting 310k at 70 and at 71 it jumped to 337k (if memory serves me correctly).

[wereotter]

At level 71 that means you're doing Shadowbringers content. All side quests in all zones this expansion are level synced to you. Though side quests also offer less in terms of experience than they did in previous expansions.

If there are no sidequests available in your accessible zones, then as people stated, roulettes are the way to go. If you don't want to wait on the queue, you can also go into the Holminster Switch dungeon with your trusts. And don't forget to bring some basic food with you (I just bring some oranges) to get that 3% experience buff from enemies defeated in the dungeon.

[Espritduo]

Do the old Stormblood hunt bills and beast tribe quests, and once you unlock themdo the Shadowbringers hunt bills and Fairy beast tribe (you don't have to complete ShB to unlock Fairy quests, just complete the Il Mheg part of the story). It is a huge amount of easy, solo exp each day for very little time or effort that people always seem to forget about. I went straight through the Shadowbringers MSQ without ever doing a roulette or fate grinding just by doing the quests, sidequests, hunt bills and beast tribes.

[Crazjtk]

0. ALL THE BONUS STUFF (FOOD, RESTED, GEAR, ARMORY)
This isn't leveling itself, but when you eat ANY food item, you get a 3% bonus to exp for 30 minutes, which can stack up to 1 hour. This is ANY food, so you can just find something cheap on the market board or stores and not worry about the other bonus stats. Additionally, when you log out, make sure you log out in a sanctuary. (Sanctuaries don't have the 20-second countdown) If you do that, your time logged off will recharge a bar of bonus EXP. At max, you can earn 50% bonus EXP for up to 1.5 levels' worth of exp. It takes 4 days logged off to hit the cap of rested bonus, so you don't get a huge boost if you're an avid daily player, but you take a couple days off you'll come back to a nice little leveling boost. Since you're at level 70, you won't get any benefit from any of the EXP-boosting gear any more (the top level one currently boosts you to 70) but there's items in-game that grant an EXP bonus. Anyone can acquire the Brand-New Ring, which gives you a bonus until you hit level 30. Also if you pre-order an expansion (not on the table right now, but for future reference) the preorder bonus usually includes an accessory that boosts EXP up to the level needed to start that expansion. Finally, there's the Armory Bonus. If you're leveling a combat class besides your current highest-level combat class, you get a bonus to leveling it.
1. DUTY ROULETTE
The queue time for each role on the duty roulettes varies, but generally I find healers near-instantly queue and tanks are usually in a mission within 5 minutes. (At least in my experience). Those are the classes I usually take through the roulettes. The "Adventurer in need" thing just means you get a small bonus to EXP if your class matches. You can still do the roulettes regardless.
2. SQUADRONS
For DPS classes, I've been having a pretty good experience doing dungeons with my Grand Company Squadron. It takes a bit to set the squadrons up, but once you have a squadron that you can take on command missions, you have a ready-made group for running dungeons that lets you set the pace. You don't get quite as much exp as doing the same dungeon in leveling roulette, but skipping the 15-minute wait on the Duty Finder probably evens it out a bit. The AI allies are so-so, but you can control their basic behavior a bit, and I haven't had them wipe with me yet.
3. LEVEQUESTS
If I'm quite close to a level goal and burnt out on dungeons for a bit, I'll do a couple Levequests to get me over the line. The limited number of chances means you can't rely on it completely for leveling, but it's at least a reasonable change of place, and takes a lot less time than a dungeon if you just need a liiiiiitle more exp to reach the level for the next MSQ.

Disclaimer: These are the unscientific findings and cursory research of a casual sprout, not definitive guides to best-in-class ways to earn EXP fastest.