I'll deal with these two since they are related. Tanks main stats are physical because most damage done on a tank is physical. There will be some odd attacks that are magic to make a boss 'interesting'. Any big magic attack is meant to be taken full or a cooldown to be used.
The problem I have with parry is that it's identical, from what I see, to block. We can't increase block rate apart from our shield. Parry is basically a weak block from what I can see. What I suggest is making parry an avoidance stat rather than a mitigation stat. Mitigation stats reduce the damage, like (current) parry and block. An avoidance stat means the player takes no damage for the attack, it misses, or if you like avoids it.
No, vitality increases health. Simple. No a big deal really. You gear for as much health so that a boss doesn't one shot you, and your healers have enough time to get you back up to full. Sadly this is the go to stat with tanks, not just in FF14 but lot's of MMOs. Better to survive more hits than make the healers life easy, yeah. IMO wrong.
Well if tanks don't go for vitality they should go for parry, after all taking damage is their thing and taking less is good right... A tanks job is not to deal damage it is to hold hate. With proper gear they can do that just fine so if you make vitality provide attack stats then what does strength so... the same? That's silly.
It's expensive because it's intended to be rare. SE redid the drop rates for G4 from lower ilevel gear because it was to easy to get. I'm casually doing my Novus scroll and have not done G4 yet while I save up gil and just do my G3 for now.
I'll agree with you, the GL idea is broken. Not after launch they increased the duration of GL but still with a game that's basically dodge it's so easy to lose stacks. Yes, the way to counter that is to increase base damage but it's a sticky plaster. Maybe 3.x will redo monks; I hope so. We need a rework not a game mechanics change for one class buff.
I think the speed stat is broken. We have god awfully long global cooldowns at a 2.5 base and it makes combat slow. For most classes it's not too bad but it is noticed when for example you're a tank and you have to do an action but if you've just hit one off it's a agonising 2.5 sec wait and by the time it comes off of global it's too late; it's similar for healing. The global is also a problem for casts. If you're almost finished a cast and you get interrupted just before then it's another 2.5 secs. Five seconds to cast a spell. Crap. Now BLM for example moving often can really hurt. They received a subsequent buff but it makes a class 'unfun' if you spend a quarter of your time casting and the rest moving.
The current conversion rate is just poor considering how little it changes but I believe that's because the global is so large. Even a two second global is much better and would mean a noticeable difference with little spell speed. TP regen would have to be adjusted but it shouldn't change rates relatively.
I believe for TP that doing your normal combo it should be close to TP neutral. Only special attacks or cooldowns should use large amounts of TP and then you would go empty. If you have no TP then you can only do a normal combo. There's a good example of this already. As a gladiator you have a stun on a small cooldown and you can stun when it comes off cooldown 'till your hearts content but... if you do you'll go out of TP very fast