Galio main chiming in here. Mostly mid, some top, and dabbled in support with him. I'm also a support main. That said, Galio is not the best support. He severely suffers from early mana costs, more so than many other supports. The Kalista/Galio combo can be fun and effective, but he doesn't synergize well with all botlanes. His shield doesn't feel as effective as other champs, such as Janna's. He does offer speed ups for chases and escapes. He's not the worst for peel, but by no means the best either. He only heals himself, as opposed to other champs that can heal their marksman as well.
He's honestly most effective in mid lane. He will struggle with certain ad champs. Yasuo is a pain with his windwall, but can be worked around. Still makes free farming a nuisance. Top is situational. If it's say a Teemo it'll be easy. An auto attacker like Tryndamere and it's going to be a pressure lane. Galio's mana can only go so far.
All that said, he's always been a niche pick. He's fantastic when the enemy team stacks ap champions. He can manage against a more centralized ad comp, but he suffers against tanks. Definitely some fun and something different in the botlane, which I enjoy.
could beat him at it... who knows.
