Could be a strange case where Pahlavi is simultaneously being over- and under-estimated at the same time. I think the likeliest case here is a milder case of the Venezuela situation: he seems to have more (a lot more, even) grassroots support among Iranians than the lame & gay Venezuelan opposition figures like Machado or Capriles or Guaido, and certainly he also seems to have a bit more of a spine than they do because he's actually called for direct action against the Mullahs (not just protests in the streets, his second call to action was to storm gov't broadcasters and such) instead of cucking out and begging for more peaceful protests when his followers were met with heavy automatic fire, however he's quite lacking in institutional support. (Which makes sense, the Ayatollah & Mullahs have had nearly 50 years to purge Pahlavi loyalists and make absolutely sure every Iranian institution from the army to the banks is crawling with their lackeys.)
It does help his position that there really doesn't seem to be any even halfway viable rival to his status as the highest-profile opposition figurehead, definitely there really doesn't seem to be anybody like that in Iran itself and abroad - hardly anyone respects or cares for (or has even heard of) the likes of the MEK. At least in Venezuela there are names other than Machado being thrown around for a post-Chavismo leader, like Guanipa IIRC. In Iran there seems to be literally nobody else, certainly nobody else's name is being chanted by the masses, and as far as I can observe the only alternative to either the status quo or Pahlavi coming back (if not as Shah outright, then at the very least as a transitory figure) looks to be an IRGC coup, soft or otherwise, and imposition of an even harsher theocratic military dictatorship (since the commies are totally buckbroken/extinct).