But, I have figured that the methods of fuzzy control can't be THAT bad. Because even with my neglible knowledge of process control I have been able to build some useful control applications. But, as you said, and I admitted, many people in fuzzy control area come from elsewhere, and have a limited field of the control theory field. Therefore the evaluation of built fuzzy controllers has not been very analytical. It is in some sense true, because usually in fuzzy controllers only the expertise of the human operator is modelled.
Nothing is assumed from the process.
I doubt it. Fortunately not all people working in fuzzy field are as ignorant of conventional control theory as I and many others are. I agree that most current fuzzy controllers are just another function approximation. But also as such they have turned out be very useful. They don't only represent the input-output relationship, but they also work as a model of it.