It's faster, written in TypeScript and has 99% test coverage along with integration tests against a testnet. I'm also aiming to simplify the steemd APIs instead of just providing a 1:1 call wrapper as shown here with the account creation.
But I understand your point. I started out using steem-js and even have a commit or two in the project but to be honest I didn't like the smell of the code... and barging in to a established project and saying "Hi! I'm new here. I'm going to rewrite all your things in my own opinionated way" usually don't go over well :) I also recently wrote a WebSocket RPC client that I could reuse a lot of code from.
Great contributions on your side. I think having a 1:1 call wrapper is necessary to have a low-level API available for different use cases but I wished we could all build new high level APIs on top of that one single well maintained code.
Even so, it's a great effort on your side and maybe it's better to use a well tested code like yours for new apps. I find it a little risky for new devs to join since most of the sample codes are for steem-js and it makes your job much harder to promote your solution.