The thing is that they are buffing the wrong things. That’s why his ult seems powerful but other than that he is underwhelming.
The last nerf they gave him was a Crystal Ratio reduction on bounces from 100% to 80%. While it seems it’s “only” a 20% (we’ve seen harder nerfs), nerfing a 20% of a hero with 220% is not the same as 20% of one with 100%.
To compare it, the hard nerf joule received when she had 63% win rate made an impact on her of ~8.63% in the TS damage, Vox nerf was a 20%, more than twice as strong, when he had a 49% win rate. Not only that but unlike other heroes his whole damage depended on the resonance bounces. That ofc killed him.
They’ve buffed his ult multiple times to give it back the damage it used to have, because again, the base of its old damage no longer works. Reason why his ult is powerful. The problem is that outside of the ult, none of his damage was given back, so you are left with a mid laner that can’t compete in damage at all, brings no cc and has low range. The buffs to the SZ has been useless for 2 reasons: doesn’t matter his mobility when he doesn’t deal damage; the energy cost was nerfed hard a long ago (which was one of the things that killed WP), so he ends up relying a lot in energy items, which reduces/delay his damage power spikes.
He is not used in EU t10 (usually) and high elo scrims because due to all I’ve said, once you dodge the ult, which isn’t too hard, he offers nothing to his team. For some reason they keep buffing his mobility, range and ult damage, but so far all that have had 0 impact because again, he lacks damage. You can’t give a hero with 49% win rate more than twice the nerf you would give to a 63% win rate hero, and that’s what they did.