I think for a lot of people, myself included, water in the nasal cavity feels terrible no matter what. I feel it's less about preventing water from entering your throat and more about keeping water out of your nose entirely.

I actually really struggle with that, and hate the feeling of water up my nose hence the plugs. Some white water kayakers I know don’t bother, but most do because if you’re play boating or running something class 3 plus the torrent of water is being forced up your nose and that sucks. If I’m just swimming I can manage with out nose plugs but it took me a couple of years in my late teens to get used to not holding my nose. And even still if I’m jumping from something higher than the edge of a pool/low diving board I physically hold my nose

Water gets in my sinuses and causes a major headache.

It got even worse after sinus surgery.

And on top of that you look like a character from the movie Battlefield Earth

I don't understand either, I can't do it manually my brain just does it anytime I go underwater. I can jump in water with my mouth open and nothing enters my body 🤷