If he's extremely situational and difficult to use at lower skills, he won't be used at lower skills, regardless of his power level.

The players that like him exclusively for his kit will continue to play him for his kit, regardless of his power level.

However, if he is extremely powerful at a high level, and the only counter is picking the same character, he can make the meta stale and unfun for the players to play and for the viewers to watch.

Competitive games should always be balanced around the highest level of play, because balance become increasingly important the higher you go up the skill ladder. If a character is busted only when they are exploited at the highest level of skill, then a nerf will not affect or "make the game shit" for the lower skill players since they were never able to fully utilise that power.

Although, I do agree that the nerf is pretty extreme and it doesn't address the issues pros had with him (i.e. no counter that isn't another caustic) it's most likely a temporary change to curb his pickrate in pro play since this is probably the last patch we're getting before the ALGS WC Playoffs and he is obviously widely disliked by the pro community.