1-
The level requirements are there to streamline the endgame content because ubers are all over the place, so that you can successfully play it without having to constantly check documentation to see what area you're supposed to do next. Plus, entering vizjun at 100 and being one-shot doesn't really provide you with much information on when you are expected to have a shot at it, "death testing" quests is not clean nor interesting.
The argument of "this quest shouldn't be locked if I'm able to do it, freedom gud" doesn't make a lot of sense. If your act 3 character can clear act 5, you still have to go through act 4, and rarely have I ever heard act 1 characters should be allowed in hell just for the sake of freedom. This is an aRPG, and requirements to advance is one of the most basic and common concepts of the genre.
There are lots more reasons for this change, another one being that the best way to play the game is now to actually... play the game. Before it was very profitable to i.e. gear check / cheese the hardest quests first (such as Void on assassin) and then trade your way into or trivialize all content that precedes it. Playing the game backwards should never be the meta.
2-
Unlikely that you'll be killing Akarat at 104.
3-
Remove limitations so sorceresses max the defensive passives and every sorceress ever uses the same spell (whichever one is best at that point)? Sounds like an improvement.
4-
If you buff "the weakest skill in the game", another skill will become "the weakest". So asking for "there shouldn't be weak skills" is really absurd. Yes we do address and improve the builds that are the weakest but as mentioned before, another build will take the spot and it's a never-ending cycle. Not much that can be done beyond that.
5-
I don't understand how finding a SSU warrants for an instant respec to try it out. It may have been the case in early median versions, but now you'll rarely succeed from an impulsive respec. Unlike SU's which generally work outside the box, SSUs require specific setups to shine. Doing an in-out double respec just to see whatever shiny effect it has or only to see "will it oneshot all if i swap skills (altho my gear makes no sense for it)?!?" makes no justice to a good item and only wastes your time.
There's long discussions about respec in other topics (as with p much every single concern you posted) so you should look for those for a more in-depth explanation of the change. As with most sigma features, no changes will please everyone and some come with disadvantages, which we consider to be outweighted by the advantages. At the end of the day, respecs online are very accessible and free in SP.
6-
There already are. And generally speaking, farming bosses is already profitable enough. It's a three-in-one, you farm for a perfect charm for yourself, chance for a trophy, and you get a charm which you can now stash and sell.
7-
So because you don't like to hunt for trophies (even though they are clearly optional due to low stats as you mentioned), they should be removed for everyone, including the people who like them. Got it.
8-
What? You can already do this in SP using tcp/ip, or online using mules.
As far as why the system of transfering items via character isn't in place yet, maybe is because it's complex and takes time to implement, not because we want to put players through extra steps.