Back when I was just an awakening baby gay, I spent everyday trying to consume every bit of yuri I could get my hands on.
You didn't have nearly as many options back in those days, mostly just people recommending the same handful of animanga over and over again. This meant that I ended up spending a lot of time getting into some rather questionable series that I wouldn't necessarily recommend nowadays. One of those anime series that would pop up frequently and I inevitably ended up watching was Saki.
I can tell you, OP is 100% correct about everything said here. If you were to only watch the original 1st season you probably wouldn't think much of it. It's a fairly standard sports tournament manga with some ecchi and yuri elements thrown in. There are some girls with big boobs, there are some men around that react to them, some of the girls clearly have sapphic feelings for each other. Nothing too noteworthy for an ecchi. But if you read the manga to the point where after the anime ended things start to get odd... Men start to appear less frequently, only the male characters that are closest to the central narrative are sometimes begrudgingly shown. The ecchi elements start to ramp up, but so does the casualness of them as described by OP. Ladies just walking around with no pants on whatsoever, and everybody treating it like it's normal. Meanwhile, you're being introduced to the fact that in this universe they've developed technology where lesbian couples can have children together, and some of the main characters actually come from lesbian unions. It begins to sink in that males are on a decline in the world of Saki as more women are starting to marry and have children with each other. A world that is gradually becoming more casual with women's bodies and their queerness. The manga didn't start out like this, but by the time you've noticed its already become normalized. The frog is boiled.
15 years later, and this franchise still holds some bizarre fascination for me. It's not unusual for me to just suddenly remember this series and think about what that absolute madwoman Kobayashi Ritz is up to these days and how much crazier everything has gotten if I were to go and look.