I think one reason for the variability in the plans is to keep you engaged. If every workout was the same with just X added you would burn out mentally and not be able to do these plans for months or years.
Personally I like the variation even if many workouts target the same systems.
One day might have wavy blocks, one might have equal blocks, another will go up or down every block etc.
Doing (mostly) the same block week after week after week would get dull really fast.
Add in the differences in workout text/drills and there is a whole extra layer of value right there.
Don’t really agree with not knowing if your fitness is progressing either.
You WILL know when sweetspot, treshold or Vo2max start to feel easier, regardless of the specific workouts varying slightly.