Hitec and Futaba require negative (-) expotential for the desired soft center.
JR and Spectrum require positive (+) expotential for the desired Soft center.
There are no exceptions to the above two statements or transmitter settings that changes the above two statements period. get those two wrong will result in an unflyable airplane at best or a destroyed airplane at worst.
Is Expo a bad thing?? Absolutely not but is indeed a very useful tool as already noted allows the flying of airplanes that would not be capable of being flown otherwise. It also allows the setup of very gentle flying trainers that many folks just want to fly gentle patterns on gentle days and there is nothing wrong with that either. I have many older folks ending out their flying days enjoying the benefit of expo that I helped them with.
John