Up until about the 1980’s, William Shatners body type would have been considered more or less ideal for a guy
He’s not what anyone would call fat, he looks reasonably strong and athletic. Even today most normal guys are significantly less fit than William Shatner at his prime. Audiences at that time had a decidedly more ‘realistic’ impression of what a male body should look like.
What changed is that in the 1980’s, Schwarzenegger and later Stallone introduced the steroid fuelled bodybuilder/actor
This filtered down and eventually developed into the expectation that every actor in an action role should be bodybuilder level ripped, and if they’re not it will be the subject of a joke (fat Thor/fat Peter Quill):
And even these guys only look like that for a few hours at a time because that kind of thing simply can’t be maintained. Jason Momoa was recently ‘fat shamed’ when a picture of him surfaced where he still looked better than 99.9% of humanity
Some people’s impressions of what an average male body should look like are now so twisted that they look at Kirk now and think he looks ridiculously out of shape, when the only thing that is really twisted are their perceptions.
It’s the same thing women have been dealing with for decades now, but it’s finally catching up to men, and is most likely having similarly disastrous impacts on the self esteem of young men who grow up to think it is at all healthy and achievable to look like this all year round: