I am a bit confused by

A men’s speedo covers more than your most basic bikini, are way harder to find and aren’t usually sold in boy’s sizes

When i was in a swimming club as a kid, we almost all wore "speedos". Someone wearing the versions with a little bit of leg on them was the rare exception. I used to be made fun of at lakes in the summer sometimes by people wearing the "bermuda shorts". Turns out it is a bad idea to make fun of someone who is good at swimming while being in the water and wearing the faster swimwear.