you cant get interupted my naut auto, it roots you and thats it. I understand where you're coming from, but honestly, galio's ulti is EXTREMELY powerful as long as you use it right, and even with out his ult he has decent ap ratios gets free ap just from countering his lane opponent which and provides a lot of utility. I think he's just fine.
I'd like a red to post on this because you absolutely can. It has happened to me. Even if it wasn't his AA passive, it could have been a dredge line in such close proximity that I missed it and it looked like an AA. Whatever the case, I'm pretty damn sure his passive broke it. And even if it didn't, dredge line can and it's yet another skill to add to plethora of abilities that make Idol useless.