I actually think the dichotomy is necessary to have a consistent framework in this sort of system.

If Thinking and Feeling weren't dichotomous, that would mean certain judgments would be impossible to differentiate, making the system pretty useless.

The reason this system works is that it divides cognition into mutually exclusive parts so that it can describe those parts interacting. That way, we can actually use the functions as descriptors for what we see people doing (or at least use combinations of them as descriptors). If the definitions were more loose, these descriptions wouldn't do anything.