The thing with the ITF schools that I visited is that they're REALLY focused on making TKD something that anyone can do, so the intensity gets ratcheted down. I remember a conversation I had with an instructor where I mentioned some things I didn't like about a lot of the ITF classes I had seen and how I "didn't think those classes were building effective fighters," and she was like, "C'mon, taekwondo is a hobby for people. It's something people do to stay in shape and have fun."
It comes down to the instructor. ITF TKD has the bases to be a very hardcore discipline, and lots of schools follow that path. ITF comes directly from the lineage of the founder of TKD, and kept his principles which were that it should be a martial art, not a sport. He was against competition because of the limited rules sets for example.
Obviously some schools will deviate and make it "customers friendly", and some school will have both. I mean they will have some softer training for some people, and more extreme for those who want it.
For example at my place, there are 2 very high level people. One girl and one guy. Both have started from very young and are now in their mid 20s. The girls doesn't give a damn about competition. She spars, and she is decent at it, but she will only spar light, since she never train for actual matches. Our instructor wont press her when she doesn't go hard. But he will if her technique is not good.
On the other hand, the guy is all about competition... So with him, the expectations from the trainer are a lot different. And so are the drills and the intensity of the training and the sparring.
So when they do the same drills, he will mostly correct the technique for the girl, and the intensity/power for the guy. Obviously, if one day she is too lazy, or if he is too sloppy, they will hear about it...
And it's not about a girl/boy thing. We a have a teen girl that is tough as shit, and he makes her train with us at high intensity, and with hard sparring.