Could you imagine the chaos this would create? Everyone who uses a low volume plan for intensity but also rides outside (which I gather is a good percentage of users), would see their PL’s drop. Do a group ride… PL drop. Commute to work… PL drop. Go for a ride with the kids… PL drop.
I think a lot of people feel they need to always be progressing. So if they see a workout that is not at or above their PL, they feel they are going backwards. But you aren’t. Sometimes you need to take a step back to keep going forward. In this regard I think the “productive” label for workouts could actually dip below PL’s some. Might help with perception of what the workout is doing for you.