I guess the argument here is that those ads are designed for men, but they're designed to prey on an extremely primitive, kind of circular logic: "you would look like this if you bought this underwear." Sort of a "this man is desirable to women, please act like him."

I am pretty iffy about that kind of detailed psychological reading into people, it's not completely clear to me that people internalize those ads in that way, and I suspect a lot of people internalize ads completely differently from each other, so I question if any of those explanations are actually generalizable. But I guess it's somewhat reasonable, maybe, to make the argument that male model ads are trying to say something like, "this is the clothing that attractive men wear, and if you were attractive you'd buy this." Or even, "this man is attractive and thus obviously has his life put together, and maybe you'd feel more like him if you had his brand of underwear on."

But I'm much more sympathetic to and supportive of extremely broad statements like, "both sexy women ads and sexy men ads influence beauty standards in sometimes unhealthy/unobtainable directions regardless of the intent/purpose of the ad." I feel like getting super-specific about what exactly is running through a man's mind when they see an ad for underwear is when we start to get uncomfortably close to pseudoscience. But the much broader statement feels a lot less like pseudoscience, it does seem fairly clear that beauty standards are influenced by advertising (and by other things too, advertising is just one aspect of this).