The difference between playing vs an overloaded and a simple champion
Overloaded example 
Gotta dodge that skill shot that slows and the super stupid return hitbox on his Q that is as bad as monster hunters Plesioth hip check.
Gotta watch his passive stacks on me or he slows me and gains a lot of movespeed.
Oh he is using his W I need to predict where it will go to dodge and not be slowed or stunned by it.
Gotta make sure I can play around his E dash.
Oh no I'm getting low on health better start disengaging or he gets more damage.
Need to watch where his ghost is at all times so that I can either dodge the ult or follow him faster to pick up the kill.
Simple example 
Gotta make sure i can position myself a little away from the minions so he doesn't get a better heal on me.
Oh there are minions and he has his E, better watch out for the double dash.
He has 50 fury, I need to play safe or he will punish me hard with his empowered abilities.
Gotta stay out of his melee range if possible(unless a melee bruiser duh).
Look at the difference, Renekton has a few things to look out for while ekko has what feels like 100 things in order to not fuck up.
Edit: you barely have to watch for Renektons stuff while you need to look at at least 5 things at Ekko at once.


.
You have one thing to think about: the range of his W.