I had a similar idea to madbob85‘s above whilst thinking about this a few hours ago.
My thinking was, instead of using ultimate laps, was using a driver’s fastest time in qualifying as a baseline, and then comparing each and all of their laps in the race against this “baseline lap,” adjusting for fuel load and tyre wear, as these affect the lap time, excluding any in/out laps, and if possible, laps where a driver had to yield to blue flags. This would ideally tell you the fastest lap a driver was capable of given the current state of their car, and then you compare that against the time they actually ran. This would show you how close a driver is running to the absolute potential of the car at any given point of the race, which (hopefully!) is solely determined by the skill of said driver.
If the effects of fuel weight and tyre compound/state can be quantified, this might be a workable idea.
(If anyone knows where I can find data on the above, plus each driver’s lap times for a race, at the risk of my free time and sanity I’d be willing to run some numbers.)
Edit: An issue I see with this is it being inaccurate for laps where a driver was the race leader, because when you’re in first you don’t always need to push to the limit.