I'd like to preface this by saying that I'm on board with the Sion rework! There is one thing that bugs me, though, which is that the knockup on his smash doesn't feel necessary. Are there any design reasons behind why it was made to be a knockup rather than just the included stun? I personally feel that changing it to just the stun would let you drop that lost power into more damage or higher stats, while also giving Yasuo less ult fuel (especially since a lot of recent champions have been getting Yasuo-compatible abilities).
While I like the direction you're going with the kit, this particular bit of his Q feels a little bit tacked on. I've read a few posts which also expressed some worry at how champions seem to be receiving more and more displacement abilities as of late, and I'd just like to echo that sentiment a little bit.
Rather, after thinking about it, I think a better question would be: Why have so many recent champions had knockups/knockbacks or displacements built into their kits - is it simply a coincidence, or has the champion team been deliberately adding a lot of displacement abilities to the game? If they've been doing it deliberately, what is the rationale behind the preference of tenacity-immune CC?
Lastly, would removing the knockup on Sion's new Q (but keeping the stun) be out of the question?
Thanks for reading! Please forgive me if I sounded aggressive at any point, I started writing this a while ago and I've been gradually falling asleep since. Hopefully when I wake up and re-read what I just wrote, I won't be too horrified.