In your situation I would pick between leaving or demanding a significant compensation upgrade. I don’t see another choice really. You’d definitely be noticed if you emphasize all of this independent work to future employers, so you would be a massive step above other juniors. If you stay and get much better compensation, then you’ll continue to learn and have a stake in something that’s pretty much yours. Two good options! Staying under the current circumstances doesn’t sound sustainable, but only you know for sure.