Why bother going offstage when you can AS him every time he can't autosnap to the ledge with his upB? You shouldn't be going offstage against anyone in general, Lucario wants to sit on the edge with a partially charged AS ready when needed.
That matchup is bad indeed, but Lucario does have genuine strengths in it too. Don't take Cloud to BF/DL and he will have serious trouble landing against AS. Couple that with his uthrow followups needing to be jumped out of (or airdodge into other followups) to safely escape after not being guaranteed anymore, he will have to land a lot without midair jump left (which in turn can send him offstage). Also, you shouldn't be trying to outcamp him with AS, just stay in midrange, utilize his good foxtrot options and have a nearly charged AS ready so you're actually able to threaten whatever he's doing. Just never challenge any of his moves head to head in neutral and maximize your juggle/landing/edgeguard punishes and you're good to go. Make him fear your aura more than you fear his limit shenanigans too.
Still, it's the matchup I'd like to play the least alongside ZSS, his gameplan requires a lot less effort to succeed and in the end, his overtuned kit poops on all of our moves head on with superior mobility. Limit break also somehow exists on top of everything to make things even more stupid. It definitely affects Lucario's viability but just how much remains to be seen, it hasn't exactly been played that much in relevant settings.