https://www.hindrajabfoundation.org/ might have some things to say in response to that. Like that it's not above and beyond to expect the mayor of a city who also presides over the largest police force in the country to ensure that the "law" is upheld in his city.

“It is clear that we do not have the independent legal authority to enforce this warrant.

Like, they literally do have that authority, they just don't want to deal with it because of the fallout that would ensue from actually doing it. We all know that "laws" are just what the ruling class want to do, and those laws will be applied selectively and bent if necessary to do whatever it is they want. Not figuratively, or vaguely, but literally. Mamdani has wriggled his way into a ruling class position and he could do it if he had the will to do it. It is absolutely not that he doesn't have "legal authority" to do it.

Edit to add: Mamdani also doesn't have to actually order any arrest, but he could just say that it's on the table as a possibility which in turn would put pressure on Netanyahu and possibly even prevent him from coming to New York. The threat alone could be enough to prevent Netanyahu from freely traveling where he wants to. It worked on Ben Gvir.