I think this thinking falls into the common belief that "sexuality" and preference within "sexuality" are actually distinct things. I really think everyone's sexual preferences are unique, and so even microlabels don't do them justice. But I don't think the purpose of labeling your sexuality is meant to be perfectly descriptive, it's a way to connect with people over shared parts of their experience with sexuality and that can be as coarse or fine as you want it to be. You say there should be only straight, gay, and bi, but we could go even more broad and say there should only be cishet and queer.