Exactly. If you run a 800PP detuned Gr. 1 (or Gr. 2 in less degree) car, focusing firstly in lowering the power, you can run FM1 with less fuel consumption (and less tire wear) than a upgraded Gr. 3 just to set FM5-6, to save fuel.
You put a upgraded turbocharger on a Gr. 3 just to put it in 800pp range with horrendous fuel consumption. Than you set FM6, bringing power levels to lower than original specs. So you are struggling with a 700pp car in reality.
Sardegna is easily done in one stop in FM1 and you don't even need a full tank to finish after the stop, no need for tires too, and even Spa 1 hour race is doable in one stop, with strategy being defined exclusively by weather.
EDIT: Very easy too with the Chaparral, probably easier even, but two stops needed. Which isn't so bad, as you don't loose to much time on Sardegna pit lane as in other tracks.