Dream Zanarkand is a physical location you can go to. It was not explained if you need the fayth to do so. The ruins at the end are of the REAL Zanarkand. The dream Zanarkand was destroyed but is likely just put up again. After all Tidus' mind goes there to meet Bahamut's fayth. Tidus and the rest exist as a memory of real people. This dream started shortly after the original Zanarkand's destruction about 1000 years ago. Notice how Tidus never questions him being 1000 years old? They don't realize it. Maybe that's way the term "dream" is used.
Because of Jecht. Jecht was really the only one (un)lucky enough to get booted off Dream Zanarkand. Tidus was on purpose. Jecht went for him. Auron got there on purpose to protect Tidus. Going there might require help from the fayth / SIN or being an unsent.
They can only if the cling to life & aren't envyous of the living. The only unsent we know of are Yevon-sheeple & Auron. Notice how Auron after being unsent looks 50+ even though he is in his 30s? He also can't use his left arm that much.
Racismn. No really. Guado are hated and also exclude themselves willingly. This doesn't help Seymour in his pursuit of more power and influence. A marriage with famous Braska daughter and nice Yuna would. If the gentle Yuna can see the good in him will you too?
Yes the fake god that is worshipped by crazy people is not omnipotent. It was explained that it takes time for Yu Yevon's control to work. That's how the calm is made. Dream Zanarkand was remade. It's a summon. If Ifritt dies once it can be summoned again. Same for the city unless of course the dreams would end. I don't know why you think that the whole point of SIN would be to preserve Dream Zanarkand. Yu Yevon can still kill in order for him to be seen as a god. Why attack Kilika if you just want to preserve a city?
Everything explainable without faults imho. Like Dynamis, hence why i never said that this part of the lore has a logical error. Please explain how the Elpis time travel makes sense. After all our intervention didn't cause anything, right? So why was the timeline Graha is from not destroyed by Meteion?