The fact that you need to store all previous blocks (and content) to fully validate later blocks is an advantage in this case.

I was super into using hashcash for antiabuse in social stuff pre-bitcoin, but the difference in hashing rate in-browser versus in C even then rendered it somewhat ineffective at anti spam as an abuser could hash 10-100x faster, and the delays on the UX side for legitimate users made it a nonstarter. With GPUs and hashing asics now that gap is even worse.

(FWIW these days the Steem blockchain that holds the steemit content is delegated proof of stake, for block production.)