We're going to be putting a QGT out sometime in the next few weeks that chats about durability, snowballing, game time, etc. that will talk about a lot of the things in specificity.
But for now, the high level thoughts on durability here are that we're not close to being back to pre-durability, but natural patch balance, item changes, new content, etc. do contribute to pulling it back some.
We expect if we're taking good swings at balance we can't only nerf things, we have to buff things as well in ways that align with a champion's fantasy (preferably in ways that aren't durability, like MS buffs to Nidalee or mana buffs to Sylas like you mentioned) instead of damage. But sometimes, the thing that is going to resonate with a Caitlyn player is their damage being buffed.
Ultimately, it's a push and pull. We track the number of buffs/nerfs we do in a patch, and the number of damage and durability buffs/nerfs net we do patch over patch.