What's the difference between 4.5 hours Endurance (your program) and 4 hours at 70% FTP?
Even though I have 'big' days, it's only 2 days a week and, even then, I spend about 20% of the total time over the weekend training FTP.
I'll agree there is benefit in spending time in the saddle at lower intensities but it's not to somehow magically allow you to train at higher intensities later on. The real benefit to time in the saddle is just that - time in the saddle. Allowing your body to get used to extended periods on the bike. Not just your legs but your butt, shoulders, back etc.
Are you saying there is no difference between our endurance ride workouts?
You almost sound embarassed to admit you do long rides (and very dismissive of my admission). The whole "time pressured" thing forcing everyone into 2x20 twice a week and no more than 8 hours / week is a bit of a trendy view of training - if you have the time available (for training AND recovery) it's not bad for you to do long rides.
I am going to completely disagree with you on the "time (at 70% FTP) in the saddle doesn't train you" stuff though. Looking at Coggan's inverted bell curve, training at 70% gives you ~35 units of stress. Training at 80% gives you ~45 units of stress. To get the same "stress" as 4 continuous hours (x 35 = 130) you would have to ride at 80% for 2:50, and 90% (50 units) for 2:36. I back up my 4 hour day with more of the same plus 2 x 20 @ 90% FTP.
I think anyone doing 90% FTP for 2:36 is going to be doing very little the next day.