Assassin Update Should Be Next
The next update should be for assassins. Generally they are feast or famine, overpowered or underpowered. An update would be the best way to address them. Give them some specialized items and make their kits safer to play as and against.
The champions I would like to see in such an update are:
Evelynn - She is in a really awkward spot right now. She is an assassin that thrives in chaotic team fights, similar to Illaoi, but only because of her ultimate which has an extremely long cool down. Otherwise without an ultimate or being far ahead she is very lackluster.
Akali - The player is either destroying the enemy team, or they are regretting picking Akali. I understand that her core style of playing will most likely always be dive in and kill the enemy carry, but to be honest its more of a kill for kill kind of deal when team fighting unless you play janitor. Another concern I have for her is a very static play style. No matter what you will always have the exact same combo unless you are on cool downs. Perhaps Riot should look into giving her some more flexible spells.
Katarina - She pretty much has the same problem as Akali. Feast or famine, and her kit doesn't really have a lot of flexibility.
Rengar - He is pretty fun to play as, and I wouldn't say that he is a one-combo type of champion like Katarina and Akali, his real problem is having one job that is very easy to stop. He typically wants to get fed early game, and then come mid game he will dive the enemy carries and allow his team to fight the enemies without having to worry about one of their carries. If he is behind early game he becomes very team-reliant and will take a long time to catch up. Although if he does have a lead he won't be able to do much against teams that have peel, this makes him a very risky pick and generally the reward isn't worth it.
and
to your list. I think both of these champions are problematic and need some tuning and kit changes in order for them to be more healthy to play and play against.