From my view, I rarely see this line of reasoning in the wild

As a example: I heard complete silence from this portion of the left during the NYC mayoral race/Mamdani’s campaign. No mention of (let alone stumping for) a more progressive alternative.

I’ve seen quite a bit of discussion about this, personally. Here is a thread on Hexbear from a week ago with people arguing back and forth over this point. And if you search “Zohran” you’ll find plenty of comments celebrating his win.

Only attacks on his international politics (not sure why that matters for a mayor)

It doesn’t really matter that much as a mayor, but it does matter somewhat if he’s treated as a leader, representing ideas beyond his official capacity. And that sort of thing is why Marxist participate in electoralism in the first place.

It’s a complicated issue.