No, I'm in the third. Sorry. There are definitely things that could be better, but not "with a little effort".

There's a lot of griping about the third act, and yeah, I get it, it's incomplete and comparatively poorly optimized. But it's still really good. :P They clearly bit off more than they could chew with the City, that maybe they could've solved with another year or two of dev time. (Hopefully, will be solved in a Def Ed a year or two down the line.) That isn't necessarily dev time they had, though. Not without taking out a ton of loans (do you really want tencent to own more than 30%?) and risking ill-will with consumers and WotC. (The game was meant to come out over a year ago.)

I've played through A3 and loved it. I don't think your "beast of a PC" is as good as you think it is.

I don't know what your problem is with Act 3. It might not be as good as the rest, but it's still plenty good and better than most modern games. I just killed >!Gortash!< after completing nearly every side quest I could find and I haven't really had any issues. Sure, there's a few things that could be a little more fleshed out or that feel like cut content, but not much. I also don't know how many of those things are actually cut content and not just references. Like in Cazador's manor there's >!a body with a note talking about a sleep potion and acid poison. I'm pretty sure it's just a Romeo and Julie reference. He took the sleep potion to fake death, his lover found him apparently dead and killed herself. He found her dead and killed himself.!< There may have been plans for a quest there, but idk.