If I am going to be completely and fully honest, swain is not in the best of places right now after the mini rework Riot gave him, he feels like he does absolutely no damage and that there is too much damage in the game for him to drain tank through like crit GP barrels.

Swain support has come into light over the last season with its ability to do lots of damage as most mage support do and for his all around great early utility. With the recent changes to the Glacial Augment rune now working with CC as of patch 11.23 which he has one sorce from with his E, but also if an ally cc's an enemy champ his passive allows him to pull the cced enemy closer to him and it counts as CC.