The anti mage theme always was pretty shallow and certainly not very important to his identity, and that's about all they kept.
You certainly didn't play Old Galio at all If you think this one feels anything like it. Old Galio was more like a battle mage, haveing rather subtle controll tools like the slow on his Q and the speedzone of his E, beeing temprorarily tanky with his W and haveing his big moments with the ult.
Now he has a dash, a semi global ult with wierd targeting, his aoe taunt as chargeup without the big final that made it feel so great on his ult, no longer ranged soft cc, no sustain, no speedbuff for his allies. He was a mage that had windows in which he worked as a tank, now he's a tank with one spamable ranged skill that tries to cover the mage like feel but simply doen't succede at that.
If you look at a good rework gameplay wise, take Poppy. She retained her wall stun-charge, she stayed rather bursty with hit n run patterns in lane, they even found a way to give her a new healthy ult that still allows to find isolated fights while her old ult was the main reason for the rework, and she still is great at diveing the backline and zoneing the carry. She feels pretty similar to old poppy in her playpatterns, the only critic there would be that she no longer can be used as a melee carry, though there are still people out there haveing succes with Ad heavy builts.
And for Galio: Yes, i think he didn't need a big gameplay update, Reworking his passive(the new one is pretty good) and some smaller adjustments to the rest of his kit would have been enough. He didn't have huge game health issues that demand drastic changes like Sion or Poppy had. A modernisation of his kit would have been enough, no full redesign needed.
then xD
=
who kept complaining that our ADC is just getting carried while she kept trying to go in solo with flash ult over walls and other shit.
combo and it was truly glorious.