They aren't OP, you're in Wood 5 elo.
While I do think there are a few champs that are oppressive at times, and there are champs that I dont enjoy having to play against(looking at you
) I often see in the Wood 5 elo im in(and deserve to be in, im not very goo atm, trying to improve) a list of champs that are constantly either complained about, auto-banned every game or simply ppl will declare gg and go afk to.
The biggest champs for this in low elo imo are

Ppl will whine and whine all game about how these champs are unfair or OP and the real reason they come off that way is simple, the people playing against them are garbage(myself included I just dont whine when I lose, if your bad you lose)
Darius is yes a very strong champ, do u know what makes him really strong? Your top laner refusing to turn it into a farm lane and not feed the Darius 2+ kills in the first 15 by hard pushing waves and overextending, He can also be SUPER strong when 25 minutes in your adc is trying to 1v1 him and stands perfectly still as she AAs, making no attempt to kite him.
Blitzcrank---Learn to dodge a skillshot, if you cant predict skillshots u deserve to be caught out every so often
Master Yi --- A large portion for this is simply that, if you can jungle at C or c+ level in low elo, prepare to feel like a god most games. Wanna gank? Have at it bcuz the only wards your enemies have places the whole game are trinkets. Wanna counter jg and farm heavy. GO FOR IT, the enemy jg is busy being executed by a jg camp and waiting 2 minutes in bot lane for a glory gank against a duo under tower. Yi just happens to be a jungler that can turn hard carry later if he gets a lot of kills/farm, its almost like giving an enemy champ 10 kills in laning phase makes them stronger or something
Tryndamere- We do understand the concept of hard CC yes? and that he cant use ult when stunned, so just stun him after u engage a bit, not before, or my personally fav "he activated ult, so unfair he cant die!" ok ok, so why are u still fighting him? Just wait for his ult, count to like 3 as u kite away, then hit ignite and run...u win.
All of these champs are what I like to call pub stompers, they arent Op, or really even super good(only darius is super viable and he isnt super crazy). They are just able to win games easier than most champs if the enemy team basically lets them do it, they dont need fixing, you need to learn how to play
