Bellows Breath being on a 17 second CD at early ranks is bad, but is hardly the worst of it.
Bellows Breath not having "unstoppable" anymore just dramatically lowers his skill ceiling.
It's like removing Maokai's untargetability frames; yeah it makes him more kitable, but it also removes a massive amount of depth from the champion.
It turned the spell from something that added depth to the champion to just another "damage in a cone" spell.
That nerf, when combined with the nerf to Brittle's duration (6 seconds >> 3 seconds), makes it pretty much impossible to deal your W's brittle damage to anybody aside from their frontline, since you're so easily kited.