Vi needs to be able to be effected by CC during her ult charge

Counterplay gets thrown around a lot, but "counter play" means more than abilities being skill shots or being interruptible. Since Vi's ult moves her to you, then your "counterplay" is basically going to revolve around positioning. If your carry is out of position, or alone, and can't be protected then yeah she's going to come slamming down on you and there is nothing you can do about it. That's why the carry should be with the team behind the front line, so if she ults them, the entire team can just collapse on her and take her out. A poorly timed Vi Ult can guarantee Vi's death, the same way a well timed one does for her target.

You do realize she can be bursted down, targeted, and still damaged, right? Being invulnerable to cc is what her ult does, being an unstoppable force until she reaches her target. Seriously, you can actually kill her mid-ult. Try it, it's hilarious.

The base damage and scaling isn't all that amazing. If she builds damage, you can nuke her or collapse on her. If she builds tanky, she's not going to deal much damage (although your best bet is to peel for the adc and let 'em take it from there).

At least it isn't as broken as Lee's R.

I think lowering her ult damage more would pretty much balance it out, since it's famous for its hard CC, not the damage.