Again, I don't really agree with you. of those I listed, Ivern, Teemo, and Evelynn are probably the only ones that can't just appear and freely melt an entire enemy team in a teamfight if fed, ... and I only include Teemo because it isn't as "free" as the others. Even Evelynn can pick targets off one by one.
Neeko's ultimate is a massive, devastating AOE that locks everyone who manages to survive down so she and/or her allies can finish them off.
A fed Pyke's R can execute targets at around half HP, .. and that isn't even the squishies. His large base health pool makes him difficult to kill unless you are also fed, and if you don't he will just go stealth again and get most of that health back.
If the enemy team is dumb enough to fight around bushes, Rengar will just one shot everyone. Without a bush nearby, his ultimate gives him enough mobility that your carry isn't safe anywhere.
Shaco will come out of nowhere and cut you in half with his backstab, fear you and your whole team and just walk away while his boxes and / or his clone finish you off.
And Wukong's Cyclone deals a massive amount of damage per second and the cc makes it easy for his team to put you down, if he doesn't do it himself.