My sister's QH doesn't like broken mouthpieces; he just seems to find them uncomfortable and irritating. He's happiest in a medium-length shank curb with a low port and roller for western, and a low port kimberwicke for English. I'd love to get my hands on a mullen mouth snaffle and try him in it, to find out if it's the snaffle action or the broken mouth that he objects to. Scout is quite happy in his single-jointed eggbutt.
Horses are all individuals; they have conformational differences and comfort preferences just like people. I love the earlier flip-flops analogy.
There are so many bit options and mouth/cheek/leverage combinations out there that there's usually something for every horse. By the same token, you'll probably run into something that just doesn't "do it" if you experiment enough. If your horse is telling you that his bit is uncomfortable for him, no matter what kind of bit you're using, it's time for a change.