I can certainly see a similarity between these people: ... and these people: ... Don't you?
Yes. There these athletes are similar. They are using the same Strength for ability checks.
There were four examples of body builders. Not shown here, but all of them are known for their heavy weight lifting. One of them is Schwarzenegger. All four of the bodybuilders appear to be using steroids. Schwarzenegger did, and he discusses his use of steroids honestly. Because of artificial hormones, none of these bodybuilders can be considered examples of the ‘natural athleticism’ that Strength represent.
Nevertheless Arnold Schwarzenegger is agile, moreso than the objection seems to imply.
Can Arnold do handstand? Yes.
Can he do handstand pushups? Yes.
Can he walk on his hands? Yes.
Can he run on his hands? Probably (but I havent seen him do it.)
Can he ‘jump’ by means of his hands? Probably better than most humans can.
Can he throw a javelin? Yes.
Can he wield a sword accurately in melee combat? Yes.
Can he play football? Probably.
Can he do longjumps, highjumps, and climb. Yes, yes, and yes. He is an action star. Many of his own scenes are examples of him using Strength for his agility - for explosive strength and body mobility.
Arnold is, in fact, agile.
Despite the fact that Arnold Schwartzenegger drank a Potion of Lifting, that gives him a bonus to Strength (Weightlifting) skill checks, his ‘natural athleticism’ shines thru, and his Strength is inherently agile and makes his body mobile.
Lets look at an other image where Strength is in use for an action, rather than just for flexing and bulging, and ‘looking cool’.
Here there are three women who are circus performers, it seems. Two of them are doing handstands and might be on the verge of doing the body folding of a contortionist. One of them is holding up one of the handstanders.
Now the one who is lifting up the full bodyweight of a handstander is using Strength for ‘lifting’ a ‘load’.
Can the two handstanders use Strength to do their handstand? Yes. But these two in particular seem to be in the situation of a Finesse check, and might be able to substitute their Dexterity instead. If these two remain stationary - motionless and nonagile - with arms locked to support their bodyweight, then even average Strength would be adequate, and they can probably use their Dexterity check for the sake of small sensitive motions. However, once they start moving around on their hands, doing handstand pushups, other kinds of body lifts like hand spins, and so on, then they are using Strength. In this particular case, if they are non-agile and immobile they can use Dexterity, but if they become agile and mobile, then they must use Strength.
Even so, these are probably professional performers and probably have above average Strength. With regard to muscles, strong women tend to bulk up less than strong men do (assuming no steroids). The women here look buff in a feminine way, and their acrobatics that involves lifting and body pushups probably uses various Strength checks.
The next image is an Olympic gymnast on a pommel horse. Yes, he is using Strength for his body lifts and hand spins. Look at his shoulders as he does it.
Next is an image of a gymnast on using Strength for a highjump. It is around the threshold but seems able to clear to clear a hurdle of three or more feet high. The higher this jump is, the more points the judges will award her.
In terms of D&D mechanics, all of these images represent the uses of the Strength ability.