Then if her winrate didn't drop much it wasn't much of a nerf.
Her winrate didn't drop much because she's still extremely easy to play. Warwick's winrate is on par of what it always has been before Weedwick after his kneecapping because he has an extremely low skill floor. Same goes for Sona. What they did for Sona is completely destroy her identity as the Aura Support for these shitty "snuggle zones", shit on her healing and movement speed buffs, and front load all of her power into her Q. She turned from an attrition mage into a cheesy feast and famine Q bot who is forced to build a decent amount of AP to do anything relevant past laning phase.
Sona's power wasn't "hidden". You could clearly see what Auras Sona had up and play accordingly. Blue? More AD and AP. Green? More armor and MR. Purple? More movement speed. I'm not saying old Sona was perfect by any stretch of the imagination, but she was a billion times better than the shit we got stuck with. Sona's rework was a failure because not only did it completely destroy her former identity, but it also solved zero of her gameplay issues. Cassiopeia and Ryze are in that same boat.
It's weird that you criticize old Ashe for having hidden power when Sona was the textbook case of hidden power and they moved a huge source of her winrate (group buffs) from stat buffs into much more visible procs
Just because it's visible doesn't mean it's better. I mean, a 0.5% increase for every 1% of missing health? Nobody's scaling is that low. Nobody. Full AP champs and full AD champs have better bases than that, and they build fucking damage. Sona doesn't even build AP (I shouldn't say that, she builds AP to function, not to scale). So you're taking the squishiest and unsafest champion in the game, taking away her range, her auras, her movement speed, her damage, and forcing her to build AP when she's not supposed to be farming.
Winrate tends to be really iffy with Sona due to her low skill floor, but I know from patch 5.20 her win rate was at 51%, but her playrate was only 3.35%. That means that only a dedicated playerbase is playing with the champion, and even then she's barely breaking even. Which means she was an extremely unattractive option then. Her being strong right now proves my point on how bad her rework is in that a small change to mana can turn her from garbage to powerful and then back again. Remind me again how that's a successful rework?
I could definitely get procs in lane after the one I got from going out to lane. That should happen naturally a couple times as long as you were last hitting instead of just constantly firing. Not to mention that in the late game it ramped up so fast that basically any amount of time between fights meant you would guarantee that you'd start the next fight with a crit.
That's my entire point! From all points in the game, all Ashe's passive was was a guaranteed crit once you got into lane, and then she didn't have a passive! Also, no, you did not get procs in lane, it was impossible unless you miss farm. It required Ashe to not attack for three seconds. And building up 4 focus per second, you would have to wait twenty seconds to crit. So I'm calling bullshit. Late game it was possible to crit like that, but the guaranteed crit was meaningless against a full build ADC, which would already have in the ballpark of a 50% chance to crit, so that extra gold value you get for being a guaranteed crit is meaningless when your opponent could easily do the same thing just based on a coin flip. Her passive was useless at all stages of the game. There is literally no real defense you can make for her old passive.