But it would - have you ever experimented with different views? I have and some are a lot slower than others. It seems perfectly reasonable for a host to be able to set a view which is more immersive and enjoyable, but slower.
I do occasionally, but, I've played Gran Turismo for 15 years using bumper cam, the second I change to anything else it all goes to pot! Am I faster using bumper cam than cockpit cam, yes I am, but that's because I'm not used to using any other view... it's not the case that bumper cam allows you to go faster, it's that using a different view would artificially slow me down... it would be no different than forcing me to use a different controller configuration.
Chase cam, for instance, should be easiest of all, because you can see further in to the distance, and place your car on the road exactly where you want it... but I have never set a faster lap-time in chase cam than bumper cam, it seems all my braking points and racing lines go totally out of the window when I'm using a different perspective.
As for cockpit cam being more immersive and enjoyable, I have to disagree on both points. Perhaps with a 3 monitor set-up it would be better, but as it is, it feels so much more restrictive than it should. The perspective is all wrong, and none of the hand/wheel movements are as they would be. Sure the concept of it is more realistic, but there's too much about it that's wrong, it just becomes.. jarring.
I appreciate that someones 'favourite' view is entirely subjective, but I think you'd have a hard time proving that any one view is faster than another.
Would you also force people to use X and [] for throttle and brakes... or are you happy that some may use the buttons, some may use the R stick, some may use the triggers, some may use a DFGT, some may use a G27, some may use a T500RS, some may use a T500RS with a stick and a clutch.... IMHO, these are more likely to contribute to a lap-time difference than the view.
There's also the question of whether using cockpit cam contributes to some of the frame-rate issues.