The splinters come from where they break apart and there's not really any reason to have that part of the chopsticks touching your skin.

But you move away from break apart disposable chopsticks in Japan long before you get to high etiquette dining. In my experience, basically every restaurant in Japan that isn't of, like, fast food tier, provides actual chopsticks instead of disposable ones.

I had mostly disposables but they were actually lathed wood. The crude rectangular cut chopsticks are terrible -- usually not for splinters, but they often break imperfectly, leaving you with two sticks with different lengths.