...legacies? I know hacks who wrote as well as him (e.g. Daniel Keyes). I might read Battlefield Earth but I've heard its total dreck. Everything I've heard about Hubbard is negative stuff.
He was a prolific but third rate author who tried to come up with his own version of psychology which was obvious junk and lead to prosecutions for practising medicine without a license, and bankruptcy.
So he added a bit of his third rate science fiction and pseudo science to it and repackaged it as a religion to make money. As religions go it is probably no more barking mad than most but to progress in the religion you have to pay lots of cash.
They need the cash for all the legal actions, both by them and against them. Scientology is notorious for its litigious nature. Their lawsuits are usually directed at former members who speak out against the church. Members are required to sign contracts in which they agree never to do such a thing, so these lawsuits are rarely trivial.