That's exactly what being a "power broker" is all about, though. You are leveraging your success as a politician, in order to advance your own policies...or in this case, get your choice of candidates elected. Mamdani is in the perfect position to get things done, and he doesn't need the DNC's upper management to even back him up on it.
I'm glad he's using that influence to get more DSA members into office. And it's particularly satisfying knowing that he's pissing off the establishment in the process.