The low playrate high winrate is an interesting case. I was actually talking with another designer, who has worked much closer with the PC team than I have, about this the other day.
It's one of those things that's tricky for me to explain in text, but here is my attempt.
Facts
His fantasy (Space Dragon) is broadly appealing.
He has a unique/unfamiliar play pattern with a high skill floor.
Success with Asol comes more from large strategic plays (roaming/ganking/macro plays), than smaller tactical plays (1v1 lane combat, mechanical outplays, flashy highlight video type stuff) that is generally appealing.
This creates an interesting (and actually more common, than I expected) situation.
A player finds the idea of the champion appealing and tries them for a few games.
Because his gameplay is unfamiliar and his high skill floor, the player does poorly and likely loses each of these games.
They drop the champion and try someone else.
Because Asol has a low playrate this player makes up a larger than normal percent of Asol games (not substantial with one player, but remember Asol has a broadly appealing fantasy that players want to try).
(Number here is made up) Say 1/10 of players that try Asol stick with him and LOVE him, they love the fantasy, his unique gameplay is something they can't get enough of him, they win games.
Basically the broadly appealing nature of the champion, and high skill floor are likely lowering his winrate... and his winrate has always been high.
This is what PC has seen with the champion, we having dov into him at this level in Wild Rift, but I suspect this is true and his winrate for Asol players is likely VERY high. This is super anecdotal, and not something the team would take into account for balance changes, but when I see Asol players on here talk about there winrates with the champion it's often 60%+.
As for your second point about not getting a buff to help his playrate. Playrate is taken into account for balance changes, but a light buff isn't going to shift his playrate. In order to buff him to a point where his playrate is average he would need a crazy HIGH (likely 70%+) for Asol players.
Tldr
This isn't an issue with his power level so power level focused buffs won't fix it. This is an issue with his gameplay-fantasy. And he would need adjustments in that area.