I'm really concerned that you guys are making the "Sona mistake" here.
That is, remember when Sona got an AOE CC that synergized extremely well with AOE lockdown teams, a tool that wouldn't normally be given to the support class?
Now you're giving the same thing to a ranged carry. Not just AOE damage like MF/Sivir/Graves/Corki/Ezreal who all have some kind of pretty hefty AOE nuke for midgame. AOE CC that's not a slow. Ashe's hard CC is largely single target unless people are stacked right on top of each other and her damage is appreciably lower than other carries.
Now you've given a carry an AOE lockdown CC and %health spell and nobody at Riot thought this was a bad idea. I really hope I'm wrong on this one.
I agree that potentially there may be an issue here - but we've had a long standing tradition of utility carries like Ashe and Caitlyn having hard CC that hasn't proven otherwise to be problematic.
Caitlyn's CC is the definition of chain hard CC.
While the spreading and the AoE nature of it may be problematic - I think Varus has sufficient counterplay built-in such that it won't be a problem and we can explore the utility carry space some more with him.
Additionally, Varus' can't quite lockdown with his chain CC due to the spreading nature and reduced effect - it tends to not be able to lock down an entire team just due to its spread profile.
That said - I agree, potentially scary but I think potentially scary things are fun to have in the game if they can be balanced and not frustrated.