I disagree with Silva and Lennah not needing Lv100, in my experience Silva's sk4 deals a lot of her damage and that Lennah's revive is the most reliable revive outside of MC's revive thus it gives her a lot of value.
I can't speak much for Lancelot and Charlotta since I've never used them but from what I'm seeing in the wiki, Lancelot would improve a lot with Lv100. Charlotta's is a bit underwhelming though.
As for the shiva or esser thing, ok I accept that. It could be generalized into
High one-foe attack damage
(which is what is placed inside currently). I picked shiva and esser specifically since they're the top dogs, yuel would definitely synergize with a lot of other chars, especially those that have their own assassins or consistently deals high damage. So I'm sorry if that's how it appeared.