As far as I know as a level 20 there are no gear level caps. I can take a level 1 to a level 20 place and they can get level 20 gear and wear it at level 1: my level 10 warrior has a few pieces of level 19 gear
It’s about the immersion; the map is not magical and the game is set in a medieval type of time. Modern maps that show location are out of question and while you could right it off as magic, i personally don’t feel it fits the style of the game
Warrior is not ment to be dps. The warrior class is meant to be a tanking class who tanks all the damage at high levels and should not be specing in dps talents over survivability. The recommended warrior talents are Righteousness, spiked shield, intimidate, and blessing of might
While this is a problem for warrior the rest of classes are fine; ive been able to take on poison red enemies with my warrior because i have the right specs for my level: Righteousness, spiked shield, intimidate, and blessing of might are the right talents; i have the first 2
Riley_D has already commented on this as well saying that 18-20 is in necropolar quests, the main story is what you should complete to get to level 20.
The rest of your points I have not mentioned are points I agree with. I hope that my comment has helped you!