Not sure if Ziggs is good bot or if it's just his overall 54.3% winrate. That's a 10% higher chance of winning, and I'd estimate a ~40% higher chance of being a pain in everyone's sides.
Lux's winrate is 48-something percent as a support, and Taliyah's is 45%. Lux only appears to do better because of her killsteal(tm) Ult.
And it's not just mages coming bot, it's everybody. As soon as Ziggs was discovered to be 'good bot' I stopped seeing anything resembling meta botlane. Is it a winning tactic? Yes and no.
On one side you have a higher chance of winning the game of champion select. When I play support I try to counter the whole team- it's easy to nullify me. My midlaner sees you've gone Ziggs, and counterpicks you, when they infact get counterpicked. The toplaner counterpicks your Nasus support, when they also get counterpicked. Once you've won this game, be sure to act like it was superior skills, <sarcasm>because it totally was.</sarcasm>
On the other side, botlane is not stupid- the ADC is literally everyone's favourite target and we know this. When faced with something unknown, wombo-combo or with high kill potential we go defensive. And we can farm or pull of a 'sustain' lane. Even against Ziggs. Yes, playing defensively is stupifyingly boring, you've ruined the game for us and we might just FF so we can -leave- (congrats?) But if we stick it through, we'll have a lategame-carry and a utlity-support-- and you won't.
So yeah, personally, I disagree that mages are strong (it's just Ziggs)- but the IDEA of early-game champs in botlane has spread- and I hate the style of play it's forcing botlane to adhere to practically EVERY GAME. =(