Two things here:
- I don't think Ashe is a problem for solo queue. Players have fun with Ashe support and that's mostly fine
- She is extremely too dominant in pro play. I'd feel differently if she was like 70% presence with some picks and some bans, but she's trending toward 100% ban. So we don't even see her in pro play and she's just a tax on bans instead. So, she has to be nerfed enough to change pro behavior.
Because she has to be nerfed enough to change pro behavior, I want to push hard enough that they will actually consider her counterable. She's supposed to be natively be weak into champions like Leona, Nautilus, or Pyke since she can't protect either herself or her ally from being chain CC'd and killed. But she has one of the highest base healths in the game. Her numbers now match Varus.
I think in terms of general frustration, W rank 5 cooldown and R cooldown overall are too low for support Ashe. This ends up being a pretty big nerf overall, of course, but the needle has to be moved because of pro play.
Then it's about giving ADC Ashe enough compensation to feel like she's still functional. Q's numbers changes are a strict buff, as is the base stat AD scaling, of course. The Q mechanic change is, I believe, good for the champion. Navori is now a good Ashe item, which is good IMO. Also, this makes AS purchases better, since she prints less attack speed in her kit and she goes Lethal Tempo typically anyway. I can be convinced that changing the new cast paradigm is directionally wrong for the champion, but it's definitely powerful in this new form.