I can understand lowering his damage to focus more on dishing out CC, but Jesus that is excessive. It's not even necessarily increasing skill cap. Hitting Zac's E in any legitimate competitive environment is usually very challenging. He's already had one of the most steep rewards for playing well in terms of playstyle, (just see Silas Kroeger rank 1 season 6 with zac, no other zac players near him, maybe 1 other in challenger). And allowing for definitive disengage if you miss your E is not exactly heightening skillcap.
Is it possible to a change of those number changes on Elastic Slingshot and a longer channel on his ultimate please? I'm thinking something like this to allow his ultimate to make utilizing instant-cast more appealing but not giving him too much consistent damage?
(Elastic Slingshot) 80/125/170/215/260 (1.0 Knockup Duration)
(Let's Bounce!) 160/230/300 (If channeling for 2 seconds, lift enemies)
Or...just don't change Zac's ult from live at all. People really like it. I mean you practically already made Rakan's ultimate the same thing, so I wouldn't imagine you're going to do this.