Senna can't have it all.
You're not gonna kill her from ADC even if those mistwalkers drop 0% of the time for minions you don't farm. 100% pro-play presence, viable in 4 lanes in pubs. Looking at several dumb things in her kit:
- 1-16% Current Health damage on second hit (remember, Q counts as an autoattack). I see no reason Senna should get this tank shredding for free.
- Second best mana regen in the game. Basically can spam spells all lane and especially all game...
- Q heals Senna, and applies all on-hit effects. The self-heal is particularly a problem because she supports herself, but this adding upon the other thing...
- Autoattacks grant 10-20% movespeed from the enemy hit. This is the same factor that busts champions like Viktor, Soraka, Sona etc. You got a damage which is a heal which is a speedboost on a ranged character.
- Her Ultimate having 20,000 speed for a 2400 global delivery of a shield. There's no missing this unless your ally tried really hard to dodge it, would at least have to burn a flash.
- Infinite scaling range with 600 base autoattack and gets Lifesteal for having too many stacks.
Not saying it should all be removed, but maybe some of this is a bit much...
EDIT: 7. Her root having the same Range and speed as Lux and Morgana while having an AOE effect for a character who already has excellent zoning may be a bit much...