3.5 was edition I played the most. It was a reason why I quit RPGs for nearly a decade because I hated it so much.
Every time I see another meme about how amazing 3.5 Tarrasque is, I remmember how amogn actual 3.5 players Tarrasque was the biggest joke. It was always brought up as definite proof designers have no idea how to make good monster. It was laughably easy to beat. A wizard could casually solo it, the same abilities people now miss in 3.5 amounted to ribbons. It was a laughingstock, forums had 100+ pages discussions how to fix it and general consensus was it';s beyond saving. It was first proof in 3.5 if you cannot use magic you're only good to roll over and die.
I honestly don't know if everyone claiming 3.5 Tarrasque is such a horrifying monster are trying to rewrite history or unintentionally proving what a broken, unplayable pile of garbage 3.5 was, if it's biggest punching bag is actually dangerous in a different, better designed game.
i can also confirm that the tarrasque was pretty universally clowned on for being easy in 3.5e. That discussion is basically what drove the whole "town built around the tarrasque" idea on the wizard forums and enworld. That said, it's probably not as bad as the 5e tarrasque by comparison
You know how the tarrasque constantly regenerates? Well what if you harvested it for meat?
in 3e, the tarrasque had regeneration, and couldnt die from negative HP. So the idea of building a town that "farmed" an unconscious tarrasque for its meat/bones/whatever was a popular thought experiment for a setting back in the day. IIRC there was also someone who took the idea and published it as an actual book at some point too (which honestly felt kinda scummy to me, since it was basically a big community project/collaboration)
I feel like people like remembering shenanigans or getting one over a shitty GM, but actually playing it was a slog especially with experienced power gamers at the same as new players. Also apparently enjoy arguing semantics to "win". Bleh
The 3.x tarrasque became a joke, but that was a result of the extensive options combined with people's system understanding - sure a single wizard could kill it, but that still needed to be played by someone who understood the system. It was a system that gave unlimited options, so if you worked out how to combine enough of them you could break the system wide open, and the tarrasque was a great yardstick for that.
Then you come to 5e's tarrasque and it's so badly designed that it's obvious from a glance that a level 1 character with flight can just hover above it and plink it down with a bow. I've seen 3.5's brought up in comparison to that, but not as an example of difficult fights in a vacuum.
The Tarrasque is a flawed creature in all editions. In case of 1e/2e, it's not immune to being stunned or being paralyzed (e.g. Hold Person), giving the party a good chance to exploit its vulnerable period. Later editions have other flaws, most of which can be fixed by giving the Tarrasque a ranged attack (similar to Godzilla, etc.)
The flaws in 3.5e actually involve power scale. There's combinations of abilities that are incredibly powerful, resulting in characters that are pre-planned rather than organically grown - and also meant that some classes were inherently better than others. At the same time, there were feat taxes that were essential for almost any character, which would be cutting into abilities that would be normal.
However, I'd be comparing 3.5e to Basic D&D. In this case, I'd most likely prefer 3.5e, simply because it's more flexible compared to the rigid use of Basic's weapons, but I instead skipped past that and went to both 4e and/or Pathfinder.
Eh, it's a playable fight in 4e. The biggest flaw there is it's not particularly exciting as an encounter.
I play 3.5 for a few years. One of my groups swore by it. It was... textured. When you call it a steaming pile of shit, I see your point and honestly agree with you. But I will say it was... completely what it was. It wasn't well designed, but it was immensely interesting. 5e is all of 3.x, but with the interesting parts sanded down. In my estimation, that makes 5e the lesser game.