Personally I dont think an exhaust driven diffuser will be that sensitive to changes in RPM.
The Diffuser is most effective at high speed-high air flow situations. In these situations an F1 engine is almost always either at full chat or nearly at full throttle.
Modern circuits dont have the scenario likely to spoil the balance whereby the engine revs drop, but the car is still at highspeed and requires the drive of the exhaust. Only 2 corners i can think of will create an issue, 130R or Eau rouge.
And that is if the driver goes off the gas totally, somthing that rarely happens in these corners.
All in All I see every team adopting this low exhaust with diffuser exit approach next year, at least until it gets banned.....
More could have been done.