But you're not looking at his actions, you're selectively referencing actions that support your theory while ignoring actions that don't. He's out there spending billions of dollars on ads promoting gun control, immigration, separation of church/state, and combating Trumpism. He's given $800K to Democratic state candidates. If he's all about taxes, then he would have endorsed Donald Trump and more Republican candidates in 2016. He'd be supporting Trump in 2020 or, at worst, he'd already be running as a third party candidate.
The conspiracy theory doesn't fit. Wanting to disrupt the nomination of a Sanders/Warren candidacy isn't a predictor that he will sabotage them if they are picked. If it was, you could just as easily suggest EVERY Democrat hopeful is a potential spoiler after the primary.
Fortunately we've got 9 months to see what happens, so we really don't have to take anyone's word for anything. I think it's a wild theory, but we'll only know if Bloomberg doesn't win the nomination.