The reason Exhaust hasn't been complained about before (to this extent) is because it hasn't become mainstream for most solo-laners up until recently.
Exhaust actually did get a major change; a reduction of 10 armor/mr is a giant buff in the early game, especially since they barely tweaked the damage reduction and slow.
But, because it took place during the League of Map Presence, it wasn't pushed into the spotlight.
The idea throughout season 5 and 6 was:
"If you're Top Lane, and not playing 
, you take
."
and
"If you're Mid Lane, and not playing an Assassin, you take
."
After Teleport got nerfed, people started looking for substitutes.
Once they realized that Exhaust could function as both Barrier and Ignite, since it could provide both safety and kill pressure within a single summoner spell, it quickly became picked over the alternatives.
The only reason it was buffed before was because Supports were taking Ignite more often. I highly doubt Riot intended on making it the optimal choice for solo laners.