Glacial isn't even that great. Its annoying AF to play against, sure -- but its not that strong.
Yordles beats the shit out of glacial. Nobles does fairly well into glacial. Anything with a strong, defined front line with a good high-damage back line beats glacial.
Just the way the game works is a direct detriment to glacial --- units attack the first thing they can reach. So put some separation between your front and back lines, maybe put half your team on one side of the map and the other half on the other side. Positioning is huge in this game. People don't give positioning enough credit.
If you bunch all your units up, then yeah -- you're gonna get screwed by the sej ult/liss ult/volibear splash
But if you split your guys up, chances are only half your team gets perma-stunned.
Or if you put all your big tanks a full space away from your back line, they'll take the brunt of the damage and your back line is good to free-fire.
There's a lot of ways to beat glacial -- you're just not using them.