Why can Tank Khazix and Tank Rengar just one shot me?

I find this so dumb. Riot is nerfing bruisers, but these are bruisers that I have never heard of and I bet Riot isn't gonna touch them. Why is a Khazix and Rengar that builds full tank but one dmg item, able to one shot me? I'm going even 6/6, it's not like I'm feeding, and these ppl are just one shotting me and the rest of my team, but are unkillable, which caused us to lose. This is very discouraging cuz ik i dont even wanna play the game anymore if bullshit like this happens.