Cleanse has gotten weaker over the Seasons, but not because of nerfs

It has gotten weaker because Riot keeps reducing the strength of individual stuns/fears and flooding the game with displacements and spammy slows.

Cleanse seriously needs some more perks if it's going to pull its weight as an attractive defensive Summoner Spell. When you compare it to the sheer utility of spells like Heal there's no comparison. Let alone the game-warping power of Flash.