Optional but it helps. For example, stunning/pacifying Copperbell HM last boss before Impact Roar saves your healer from using a Medica. It would not make much difference anyway - the healer will probably have enough MP to use at least one Medica, but you can at least help the healer save 400-something MP.
Paladins don't have skill management as much as Warriors do, but at least they can still do something like I described above. That is an example of a good tank. An average tank will dodge AoE and 123, but do nothing more. A bad tank will eat every AoE and put more work on the healer.
T5 in particular...neurolink positioning? Snakes positioning? This is not something that you can "macro". This is something you practice over and over again until you get it right.
I concur, it's not "mega easy". It's easy to play a Paladin. But healers have as much responsibility to top up the group as much as the tank has to keep the rest of the party from harm where possible. Knowing mechanics simply isn't enough, Paladins need to know how to manage cooldowns, and Warriors need to know how to manage buffs/debuffs.
Usually in this case, a Warrior is the better MT for Twintania, because of Inner Beast. Paladin can do the job too - you need to time Stoneskin right, it is just more dependable on teammates (ie. Virus).
I started out playing as a Lancer up till 35, before I switched to a Gladiator. My motivation was because I enjoyed running dungeons, and the 1 hour queues for Brayflox (one of my favourite dungeons) was simply too long. As a tank, it only takes me 5 seconds to get in. So yes, up till Brayflox, I knew the mechanics of every dungeon. Your friends who started as a DPS will also know what a tank needs to know, just like I as a tank know what my DPS/healers are supposed to do too.
Warriors isn't that much harder to mess up either. They build more aggro than Paladins, so it gives you more time to apply debuffs like Storm's Eye/Path, and keep Maim up. Every tank is on healer mercy, like it or not. A bad healer will cause the tank to die, which eventually causes the party to be overwhelmed. Similarly, a bad tank will fail to keep aggro or Provoke (a bad WAR may not even level PLD to 22 for Provoke) mobs off, and eventually the healer falls first, then the rest of the crew. Everyone has their responsibility, once again this is a team game.
100 hours? Gladiator was my first class when I moved over to Tonberry, I sure did not feel like I took that long. Like you I had no 50 bonus EXP too.
Killing enemies isn't so bad. They don't threaten you enough to make you feel endangered anyway, and your DPS isn't THAT low. Stop exaggerating.
Some say Titan HM is the most boring fight for a tank. You just stand there, never needing to move except during transition, and eat every bombs. For me, I made it fun by finding the blind spot around the bombs, and dodging all Weight of the Land when at least 3 other players are down. I feel a thrill pulling 9 or 10 mobs in Turn 1 after ADS/before Caduceus, and dancing around their AoE.
It really, really sounds to me like you wanted to play a tanky DPS class. Once again, your purpose is to get more people to play tanks, and I keep saying that unless people want to take the responsibility, it's not going to happen. As long as people hurl insults at new tanks for making ONE mistake, they will probably not be encouraged to play tank at all anymore. Ever heard of those stories where people cry over a game, because someone insulted them for not being able to tank? THAT is why people don't want to tank. Not because "DPS too low lol" or "name not flashy lol". You want more people to play tank? Run a tank training clinic. Go on other classes on low level duty roulette. Teach that new tank how to pull mobs. DPS is the least of the problem.
I can tell you that being overgeared for such content, your DPS isn't going to be that much higher either. I am full i90, and my Rage of Halone only hits T4 Dreadnought for 375 damage with Sword Oath and Fight or Flight. But no matter, my job isn't to DPS anyway, but I contribute what I can. Perhaps if you want to deal more DPS, go for a pure STR build? Use STR gear? That's part of itemization, don't expect to do something when your role is clearly not meant to do it anyway.
Keep missing the point of why people don't play tanks. You're attempting to fix the part that's the least problem - attempting to get the community to be more patient to new tanks is what you should be trying to do.
Here's a few links for your discussion:
http://eu.finalfantasyxiv.com/lodestone/character/175326/blog/773080/
http://eu.finalfantasyxiv.com/lodestone/character/6432645/blog/855066/
I'm sure you can find more on the Lodestone.
Or you can even try something like this:
http://eu.finalfantasyxiv.com/lodestone/character/175326/blog/790474/