I have recently questioned the importance of Endurance rides as part of a program too. Although I wasn’t specifically looking at long slow efforts like the ones mentioned in the thread - mainly just the 60-90m Endurance rides as part of the Build program - I have come to realize that I now categorize them from ‘junk miles’ into ‘consolidation miles’ whereby my body gets a chance to rest from the higher IF workouts like the VO2 and AC workouts (which have lately ‘almost’ broken me physically and mentally!) and to consolidate the gains I have made in other sessions during the week.
I outlined my most recent learnings in this post below:
Trading out scheduled Endurance workouts and trading in Sweet-Spot workouts