Pyrenean Wolf wrote:
https://www.triathlete.com/2018/09/training/the-science-of-80-20-training_334579 With the right definition of slow, it work also for bike.
That article assumes time is unlimited. For most, training is restricted by hours available in a day and time required to recover properly.
That article uses HR - 60% of MHR for me is easy Z1 and not aerobic yet
If OP is doing 5hr weekend rides and 15 hour weeks on the bike, then I agree that a disproportionate amount of those hours should be done in a z2 pace. But not 80% split between Z1-3
But OP has ridden 1300 miles in 10 months. Call that 32 miles / week. His ask of getting stronger isnt resolved by riding 80% slow