a semi auto that shoots a "revolver caliber" is extremely expensive and usually quite large and unwieldy.
Certainly some of them are, but we've already established that not all of them are, and if you accept the .22 rimfire as a "revolver round", which, I do, then you can find lots of examples where the revolver is more expensive, and often larger.
Magnum semi autos are larger and heavier than same caliber revolvers, generally, that's the nature of the beast. Magnum revolvers tend to be larger and heavier than the same barrel length and caliber in my T/C Contender single shot.
Sticking with just the .357 and .44 Magnums, for a moment, I have 4 different handgun choices, by class for either. Each one is different from the others, some radically so.
Single shot (Contenders), SA revolver (I have Rugers), DA revolver (I have S&Ws) and semi autos (Desert Eagle, LAR Grizzly, and in .357 also the Coonan)
Each one is different, grips, barrels, triggers, method of operation and quirks.
Each one does something better than the others, and each one doesn't do something as well as the others.