I get that, but it’s see it as flawed due to the implied/forced associations to training zones/levels:
If I end up with a Threshold workout on my calendar that is well below my ability, and proceed I smash it with ease, I am rating it as a 1, not a 3.
Conversely, If I end up doing a 4 hour Endurance ride on the trainer and end really worked over (prehaps I have maxed out at 2 hours previously), I think a 3-4 is very appropriate.
Point being that those numbers you suggest (yours or Coggan aligned) assume a “proper” workout on the schedule that aligns with the rider’s current ability. That is largely the goal of AT, but there are certainly times where there will be intentional or unintentional differences in the AT recorded PL of the rider, and whatever ends up on the calendar.
As such, I think your suggestion works when everything is “perfect”, but fails to handle the times when those differences exist, or days when we notably exceed or fall short (while not “failing” enough to trigger a Struggle survey) of the prescribed workout.