This is actually incorrect unless you have a vacuum leak(except in your car where that doesn't matter either). There are two popular ways of metering air and injecting the proper amount of fuel(we'll ignore the O2 sensor for now). Most systems use an air flow meter(mass flow) and that is enough, with IAT(intake air temperature), to determine how much fuel is needed.

Your Cavalier(as does Honda to date) uses a system called speed-density which uses IAT, manifold pressure and throttle plate opening to reference a pre-programmed table for fuel injection parameters. Adding any boost in your car would increase what the MAP sensor reads regardless of a change in throttle position(altitude changes cause this kind of thing) and it would adjust accordingly.

Yes the turbo itself is a restriction but maybe only for the spool up time? after that it starts to flow exhaust gas pretty well and helps scavenge.

I have a Turbo which has a damaged compressor, this is killing my fuel EF right now and its not balanced, another problem, turbos need to be in 100% working condition for it to help, and the off turbo performance sucks big time.

Why has no manufacturer made a heat recovery system from the heat on the manifold side?

Imagine some kind of closed looped water system getting heated from the exhaust manifold, it could turn an alternator for free?

I don't think I could use it to help the engine directly unless I put steam into the intake :)