Unpopular opinion incoming:
I actually think all of these champions are fine. Even Galio is somewhat unique and I really like his passive and ultimate. The only problem he has is that he is extremely ugly. Like super ugly. Give him a visual update, new splash, new ability icons, new ability particles like you did with Morgana some time ago and the dude is ready to head back to the Rift.
I feel like there is nothing that prevents ziggs, zyra and all these "classic" mages to be strong again. The usual buffs and nerfs should be enough to make them relevant again. And there is also meta shifts too. The stance of items, game pacing and popularity of other champion roles plays a big factor imo.
The only 3 facepalm examples of "holy guacamole, these champs are an embarrassment" are Urgot, Yorick and Taric.
They should shift their effort on making the new client happen and fixing the dynamic queue.
(And a sandbox mode please. Yes, I'm one of those guys.)