As others have said, each has its purpose.
I think it is a huge problem though when a rider cannot sit the canter. Because if you cannot sit the canter, you can’t ride half seat or two point correctly.
I see a lot of young riders who are just basically being thrown around in the tack slamming the horses back. Can’t sit and can’t stay out of the tack. It isn’t proper half seat if your butt slams the saddle.
My jump coach had me master sitting seat and only get into two point for jumps. I noticed on her own show videos she tends to sit between jumps to settle her horse.
Now that I mostly do dressage, its sitting in and that gives a lot of control at the canter. You couldn’t collect or half pass or pirouette in half seat!
I have a new jump saddle however and am finding its a bit harder to sit in at canter compared to my dressage saddle. It can be harder to sit in if your stirrups are really short.
But sitting the canter is the foundation of other canter seats.