So on Stargate Universe, Lt. Vanessa James is one of the biggest ass-kickers on her squad of space soldiers, frequently taking down opponents much bigger than herself. Well, bigger everywhere except in the chest department. See, James actually has a pretty small frame. She's TOTALLY in shape, but nothing about her build screams "physical strength." But that's why the show makes sure we get a lot of shots of her in just her T-shirt, which always seems one size too small. It's almost as if the show is trying to tell us, "No, no, she totally has muscles. They all just... migrated... into the breasts...? It's a thing, shut up."
You also have characters like Galatea from Justice League Unlimited, a stronger clone of Supergirl but happens to have a much larger bust than her. On its own, this would mean nothing but let's keep looking at examples. There's the case of Rose Quartz from Steven Universe, who's arguably the strongest character on the show and also sports the largest sports bra. She also is physically the largest, so it might be a coincidence, but what about Ty Lee from Avatar: The Last Airbender? Super strength, tiny body, breasts for future back problems. (Is that why she never showed up on Legend Of Korra?) It all seems to fit some kind of pattern.
A particularly weird example of this comes from My Super Ex-Girlfriend (part of the EGCU: Ex-Girlfriend Cinematic Universe), where Uma Thurman plays a superheroine who has an average-sized chest in her civilian persona but looks like she's wearing a necklace made from soccer balls as her super ego G-Girl and it's never addressed in any way. Because in Hollywood, big breasts are just a "normal," universal shorthand for super strength.
Hell, on The Boys, The Seven have three female superheroes: Starlight, Stormfront, and Queen Maeve, whom we've just listed in terms of their superstrength (from lowest to highest) and how much their costumes accentuate their breasts, unrelated to the actresses' physiology. Maeve is physically the most powerful, and therefore her costume makes her look the most incapable of sleeping comfortably on her stomach. Interestingly, Maeve is an obvious parody of Wonder Woman, and it's very possible that this entire weird trend started with her.