I understand that about "broken", but that does not describe Galio. And actually, the problem that you are describing has nothing to do with his kit either.
Galio being dealt little damage from a mage is because he is a tank and he itemizes heavily into magic resistance the same as any other tank, and similarly other tanks also are dealt little damage from a mage if they itemize like he does. Especially if said mage has not gotten any Magic Penetration. "By that I mean mages deal borderline no damage to him, but AD champions melt the guy." is something that occurs when a tank buys only MR and doesn't get armor against a threat that is AD like any tank should.
The mistakes in itemization made by players in that game are unrelated to the specific champion's kit.