World's 2016 Shows a Problem Riot Has Admitted Exists, But Stopped Addressing
About a year ago Riot spoke about niche champions vs generalists. (I don't remember what prompted it. I think it was either the Cass or Sona rework).
They said as long as a niche isn't sharply defined or a generalist is just too strong, the generalist will always see more play because they're just more useful.
Fast forward to today, where supports are by and large balanced with each other. You see Nami being picked constantly.
The solution is not to nerf her, it's to change her. Nami can heal, speed up, poke, stun and initiate/disengage even from across the lane.
We don't need a longer CD or higher mana costs or lower healing. We need to cut something she CAN do and make some other things she does better.
As an example, you could replace Nami's E, which does poke damage, slows the enemy and speeds up the affected ally, with a pure disengage like a short range knock back that centers on Nami so it can't be used offensively unless she gets behind you.
Or maybe poke is her thing, in which case you could replace her E with a line skill shot that does magic damage.
Or maybe the speed buff is her thing, so you remove the healing from her W and double the MS her passive gives when it bounces off an ally instead.
Riot. You KNOW generalists aren't healthy by nature. The Lee Sin rework you proposed shows that. So A) Stop making generalists at all, and B) Guve minor, Draven sized reworks to the generalists who already exist.