I've only played 2, 3 and 3.5. Read the rules for 4 when it came out and was not impressed in the slightest, and neither was anyone else in my group. Haven't even bothered with 5 except in the case of BG3 which uses it so I don't know if it's as simplified as 4 or if the simplicity was simply the video game format.
We never used a terrasque and it's not like I read every monster manual cover to cover. I'd skim through, see a cool picture and if the description of it was cool enough, I'd use it. The terrasque didn't pique my interest by its appearance so I never read anything else about it. I'm a huge fan of Modons though. Fuck yeah! Shapes!