Proof-of-Brain, has been proven a failure, at least in its ideal form. It is, however, better than just wasting power like PoW.

Proof-of-brain is not an alternative to proof of work, delegated proof of stake (DPoS) is.

Proof-of-brain and content voting generally could be turned off entirely and the Steem blockchain would continue to run, apps which don't rely on the voting for rewards such as SteemMonsters and others would still be working fine, etc.

Proof-of-brain was one feature added to the Steem blockchain intended to help it attract users and grow. It worked to some extent but its effectiveness to date has been fairly limited.