Most players are not "MMO veterans". And even "MMO veterans" won't slog through a crappy early stages of a game just to get to the end game, seeing as they won't know whether the end game won't be even worse.
The only ones not affected are those that already have a reason to play end-game, like a friend that invites them and can vouch for end-game being good.
And you saying that I'm wrong on this point is pretty amusing, seeing the number of games that go under due to players not sticking to them because the early stages of the game don't appeal to them.
Humans are copycats. If someone is doing something better than you, you copy him and thus become better yourself. That works on a subconscious level. In group content, if you manage to notice another player playing better than you with a class you use, you're very likely to start mimicking him...unless he's an asshole. At later stages of the game it's a bit too hectic to depend on it, true, but early on it's far easier.
They way you worded it seemed to imply something else. That it was the original posters idea, but limited only to class skills. And under that assumption I answered.
If you mean that lvl1 character will have ALL of the class skills, then that's another problem. Lack of any progress from 1 to 30. That too would have players lose interest in the game at early stages, reducing player retention.
If it's broken, fix it. Don't break it even more. As I said earlier, the current way it works is most certainly broken, but it is broken LESS than the suggestions being put forth.
The sync function should be better fine-tuned to make players find some challenge in all of the content. At that point, the experience reward should be set more appropriately. This is what pisses me off in FATE's. The higher the level of FATE the less relevant the few levels above it are. At lvl30 FATE you can already be pretty badly beat-up by the enemies, not much less than at lvl50 FATE. But the experience you get for similar level of difficulty is absolutely horrible. If you're syncing down the players stats and skills, you need to sync up the experience accordingly. The time taken to clear a FATE, the feasibility of clearing it solo and the like should be taken into consideration, not the original level of the person. Since that original level does not exist in the FATE. The same is in dungeon. If the sync would make Sastasha a challenge, it should give experience at about 70%-80% of duty that's 3 levels below you. Less because it's easier to play your character well, but still viable since it would be challenging.
But it's not. It's a cakewalk even with syncing. And that's a problem that needs fixing.
That's the problem. I am all for making fundamental parts of the class available early on, as I said before. But not the entire toolkit (not even from the class alone). There still needs to be some instant gratification for leveling in the form of skills. But an AoE, some sort of cooldown and at least one full rotation, one ranged attack should be already available at lvl15. This is something I can get behind. Dumping of skills...not.
Yeah. The moment Stormblood hit, playing below 50 for all classes went from bad to horrible. But that's proof of what I am talking about, not you.
Developers of FFXIV simply have this ridiculous notion that you promote that end-game is "where it's at". And that's what kills early stages of the game, even though technically if they were fun two years ago, they should be fun now as well. There is nothing in humans brains that makes old content unfun until AFTER it is done repeatedly. It's the developers that do it by making the old content play differently than it was designed for to cater to the end-game.
I enjoyed leveling classes before Stormblood more than I do now since the point at which the classes seem to have a fine selection got pushed back by at least several levels. And for some classes, they lack core, class-defining abilities until their 70th level altogether...
All dungeons are set for 15-20minute mark, in general. And it's going to be that way with new or old players. The only way to exceed 20 minutes is to have a player that absolutely doesn't know what he's doing (like a tank that never uses Flash/Overpower and only attacks a single target all the time) and/or a full team of badly undergeared people. Only way to do it faster than about the 15 minute mark (it varies from dungeon to dungeon slightly, Sastasha for example have a lot of walking and stopping points with keys etc., so it takes longer even unsynced than other dungeons) is to have a totally spot-on team that is not only fully decked out but also goes about their business nearly-flawlessly.
The early dungeons are a slog only because you lack AoE attacks. Later in the game dungeons are a slog only if players don't USE their AoE attacks. Or are severely undergeared. Fights themselves are rather short. Hauke Manor for example is going to take you ~8 minutes (...or was it 10 for Hauke?!...sorry, I don't remember which, but roughly 5 minutes less than doing it with a good party if memory serves) unsynced, provided you have spammable AoE attacks and go from one wall to another. Even if you one-hit everything, there's just not THAT much you can cut on other than the bosses. And bosses are actually the most fun part of the dungeons.
So, yes for redesigning classes to have well-thought of kit from early on. No for sync that gives any player a skill that another player does not. And no for no skill gains for the entire early game.