Mike Mentzer spoke some facts to a degree, but let’s not forget that he built his physique on volume training before he ever got with Arthur Jones. So did Casey Viator, Ray Mentzer, and Boyer Coe. Mike was Arthur Jones echo, his cash cow when he was marketing his nautilus equipment.
With that being said, Mike spoke some truth, but he got carried away with it. I’ve been in the gym over 30 years and recovery is definitely harder, but I don’t need 3 days off between each lift. If Mike was alive I’d like to ask him “why the fuck even train at all?” You think 3 days off is a lot, in heavy duty 2 I believe he even advocates taking an entire week off between lifts!
What works well for me, which is SOME Mentzer principles would be A being upper body day and B being lower body days. Week 1 would be A,B,A, week 2 being B, A, B. So I do throw together a full upper body day with each exercise being 3 sets usually, and a lot of muscle groups are hit intensely with just 3 sets total, then on to the next muscle group, but I also do cardio 6 days a week rt now. Mentzer said cardio was a waste of time, on that one he was totally full of shit!
Find what works for you, that guy was a know-it-all that hung off Arthur Jones dick. He built his physique with volume like everyone else until he worked with Jones. After that, half of what he spouted was marketing bullshit!