If it was the case that PV equaled TS, then that means that half of your internal energy is heat, and half is work, so at best, you are using half of the internal energy to do work.
i.e. PV = -(U-TS)
If TS = PV, then the most mechanical work you can get out of your U is 50% of your internal energy. The only way to get 100% work would be to eliminate heat. The only way to do that would be to eliminate entropy. If you can eliminate entropy you will get a nobel prize and we will have to rewrite all of the textbooks :)