Yes, I don't think that it's the actor's fault either. I should have mentioned it. I totally agreed with all that you said.
I think that if this were a different kind of movie, then the new Scotty could have worked.
I think that the former actors didn't have much to work with, because of the limited budgets. I also think that a lot of the success of the characters happened because of the former actors just selling it with all that they had. Maybe I'm out to lunch when I say this, but to just rewrite the Scotty character, but give many of the other characters similar characteristics, really discredits the work that James Doohan did.
For Uhura, she wasn't consistent with the former Uhura, but she was still a high status character.
As I write, I just thought of something. You said, "I get the possible need of water pipes in engineering". I argue that there was no need for Scotty to get trapped in the water. A running theme of Star Trek, is that no matter where you want to go, you never end up in rock or in a wall or floor. We could argue about how realistic it is, and I do acknowledge that transporters were new for the reboot's time period, but the audience has already bought into it's reliability, so to stick him in water just for humour might not be such a good idea.
Another thing about the old Scotty is that he was just a supporting character, and for the most part didn't need lines like, "I like this ship, it's exciting!".
Another thing that I found so odd was Chekov being able to ramble off a lot of scientific babble. I didn't think that he would know that. Those lines should have been given to Scotty.