tl;dr
U mad?
Actually, I did read it all. There's nothing really to argue against you about. You present valid points. I just ignore those negative points of the game as much as possible and play it. It's just a game, and I play it to have fun. If I'm not having fun, I don't play the game. Pretty simple. I'd also like to note that the game is still fully and actively under development, and as such I'm actually amazed by how few bugs there are. That's just my opinion; you're free to feel however you want about the game.
Also, I have one thing I'd recommend. Try a 2x2 or smaller embark, and lower pop cap so no migrants past the first 2 waves come. Seal up the fortress, before or after the migrants arrive. Efficient pathing can also help improve FPS. That, or set your FPS cap at 30. I've seen people play like that; it rarely goes below that, so if you're used to 30, it really helps.
I run short-lived fortresses, mostly. I rarely see less than 100 FPS, and almost never less than 60.
EDIT: I ran that save. I got between 25 and 30 FPS. Your main problem is definitely size. 219 dwarves, several layers of the site almost entirely taken up by the fort. Discovered caverns also factor in there. Unless you get something like 4 FPS on this map, I think your situation is pretty normal. Even if it's that bad, a minor computer upgrade could go a long way. Like I said, though, I prefer shorter-lived forts, so I can't comment too appropriately on your playing style.