At least from my point of view, mostly because I want XIV to be XIV and not XI again. I didn't have fun with XI at all so if XIV becomes XI again I'm going to have to quit. This game has potential to be so much better than that.
There were some systems from XI that would work if tweaked for this game but most wouldn't. This is an entirely new and different game, for better or worse.
As for OP's complaints:
Classes and jobs aren't going anywhere if the new site is any indication (they're all still there). How they work may be changed as we've seen Dragoon has some new skills so it's likely that class and job abilities are being revamped again. Hopefully this will make them work better in the role they were designed for. As it stands the intent is that classes are for solo and small parties and jobs are meant for full parties.
Class gear was released to keep classes from going completely obsolete. With that gear people have the actual option of potentially using the class in end-game content as opposed to the job. There are pros and cons to each and with the class specific gear they won't be completely useless in spite of their pros.
Tiered spells went away because they were redundant and unnecessary, at least in the eyes of the new dev team. I agree that there's issue with Fire being the AoE spell and Thunder being the single-target spell. Perhaps we'll see changes made to that with 2.0, we'll see.
As for the need for sub-jobs, in a way we already have them it's just different. Each class can take a plethora of abilities from any other class. All jobs have two other classes (aside from their base class) which they can pull abilities from. Thus having those classes leveled helps you out on your job. It's a different but slightly similar system.
As for the gripes about BLM being awful, I just don't see it. BLM is used it practically all end-game content in some way, except for Hamlet I guess. It is always viable and useful. It is, at the very least, rarely shunned in end-game content.