It doesn’t seem like there’s an especially substantial call for the 25th Amendment, buuuuuut the 25th isn’t strictly a downgrade to impeachment:

• First, yes, impeachment is only 50% House, 66.7% Senate. Boom, out, donezo. Taking the numbers alone without any other context, that’s easier than VP, majority of department heads, 66.7% Senate, 66.7% House (which is even more far-right than the Senate).
• However, when invoking the 25th, the VP and a majority of department heads are the ones who initiate the proceedings, and there’s an active, visible struggle for power within the Executive Branch.
• If the cabinet were to effectively throw a coup (because let’s be honest: none of the ghouls in Trump’s cabinet give a flying fuck about his ability to execute the law and would not be in it for the betterment of the US), then it gives a major swing in credibility compared to just a House impeachment. This is especially true because Section 4 has never been invoked.
• I would argue for this reason that, while removal of Trump by Congress via impeachment is functionally impossible, public opinion would swing wildly if Trump’s cabinet started 25th Amendment proceedings, and it also puts the initial onus on Trump to establish that he’s capable rather than the onus on Congress to establish that he’s not (or rather, that he committed “high crimes and misdemeanors”).
• Thus, you can maybe swing for the fences with the 25th if you can convince enough of Trump’s cabinet that Trump is a sinking ship (and thus Vance becomes POTUS, debatably in his own self-interest). Impeachment isn’t overcoming the numbers game, but the 25th could (just potentially) change the numbers.
• It’d be divide-and-conquer: the Democrats all want Trump out of office ASAP (obviously, because they’re sane), while the Republicans in the House and Senate would be reckoning with siding with Trump or siding with his cabinet (and whoever their supporters are) – all while the general public bleeds remaining faith in Trump as even his cabinet are challenging his fitness, and while the question at hand is a lower bar than “high crimes and misdemeanors”. In an impeachment trial, it would just be “Democrats or Republicans” to the Republicans.

TL;DR: The argument for the 25th is that, if you can get the ball rolling, it might actually be possible compared to impeachment proceedings which currently, inarguably, are not.