I like this photo because the only thing that isn't cis-heteronormative about this photo is the size difference between the masculine partner and the feminine partner -- and maybe the choice of underwear for the masculine partner, it's not really seen as crazy masculine to be in briefs. For example, the feminine partner still has shaved legs. So if there's anything that is causing you to look at this picture with semiconscious discrimination, it means that you subconsciously believe that the sexual dimorphism between those assigned female at birth and those assigned male at birth is so strong that there should never be a masculine person who is smaller than their feminine partner.
But the title of this post and the discourse so far is completely heteronormative; masculine gay masculine men do not compete with each other to be the bigger one in the relationship. Vice versa for sapphic relationships. And in most queer relationships (and a growing number of cis-hetero relationships) you would be looked at strange for trying to mog your partner on the basis of body mass. But such an expectation exists for mascs who are with feminine partners. To the point that feminine people will starve themselves (making them more susceptible to illness, literally hurting themselves, and self-destructing) to make it so that they have the dainty feminine look.
From much experience in the ballroom dance community (which is overwhelmingly cis-heteronormative), many (normally cis) women feel very guilty about it when their partners who are (especially cis) men cannot lift them for stunts. Why should we let our weight make us feel shameful, for a masculine person's lack of strength? Why does it matter?
I suppose you can surmise my answer to these questions from the title: we shouldn't, and it doesn't matter.
Yeah, this is what men should be a lot more focused on, men should all live by the motto of your friend Spider. The insecurity of the straight man is so harmful, not just to them but to everyone around them. And, uh, I hope you're comfortable and consenting if he's whipping his dick out on you lol!
It's Spider, he knows I have washed and dried more dicks than some porn stars. I used to be a nurse's assistant. Everybody I know ends up wanting me to look at something somewhere they'd rather not anyone see. "Oh, I have a rash on my junk, but I don't want the doctor looking at it, or the nurses. I know! I'll ask south, he knows what dicks and buttholes are supposed to look like!"
It's a curse. And a blessing