Lets look at Assassins

So, by the game's list, the Assassins are: Akali, Ekko, Evelynn, Fizz, Kass, Kat, Kha, Leblanc, Master Yi, Noc, Nid, Rengar, Shaco, Talon, Zed

https://www.leagueofgraphs.com/champions/stats/by-winrate

Shaco, Noc, Fizz, Zed are in the top 20 of all win-rates.

Shaco, Noc, Fizz, Zed, Talon, Ekko, Kat are all over 51% win-rate. 7 Champions. (There are only 36 total champions 51% or better; Assassins make up 20% of them)

Eve, Kha are at 50%.

Rengar, Yi, Akali are 49%+.

9 out of the 15 are 50% or better. 4 out of the 15 are in the top 20. 1 in the top 10.

Only 3 of those champions have a poor win-rate. Kassadin, Nidalee, and Leblanc, at/under 47%.

If you are an assassin player and struggling, its on you.