I consider it toxic, because there's no way to play against it. You can't stack armor or health.
There's a lot more to counter play than wearing the right padding before getting hit in the face.
You can move out of the way so you don't get hit in the face.
You can poke someone from a distance they can't hit you back.
Also: as a fan of games like Spyro, Castlevania, Mario, Crash Bandicoot, and Starwars Battlefront where there is no gear-scaling in the game at all and all damage is essentially %max HP damage by extension: not seeing %max HP damage as toxic in any way.
Considering the depth LoL offers outside of face-tanking all your problems away: you might also want to consider ways to deal with problems that don't involve face-tanking.
Tryndamere is interesting. In theory, the concept should work. I don't think people dislike the champion because of his splitpush style of game play, but how RNG based it is.
In practice, it doesn't.
In theory: LoL is also a 5v5 game that pretty much always ends at the back of a 5v5 fight, rendering good dueling potential at the expense of team-fight potential pretty devastating.
Also: it's pretty annoying facing champions like Tryndamere that have a shtick of winning 1v1 fights. In Tryndamere's case it's more 25~30 minutes in that starts because his early game is nothing short of terrible, but still.
It's generally less annoying fighting against champions like Shyvana, Mundo, and Trundle that are ok at a wide range of things despite being pretty solid duelists: as there's more outplay potential and when you die to them it tends to feel more fair, rather than someone's pet hamster scuttling around on the keyboard and winning a duel anyways because the game's code says so.
While having a natural advantage in duels has a place in LoL due to the game's balance being about blowing up the Nexus rather than being a 1v1 area, going to far in dueling potential (which is pretty necessary at the expense of team-fight potential) really isn't any fun for anybody.