the RPE stuff is an unnecessary complication

there's a big trend in modern 'scientific' bodybuilding for worrying about fatigue. the problem is that if you observe an average gym, people are way more likely to undertrain than overtrain. people just like to think "if anything, my problem is i work TOO hard"

look at pre-steroid silver era routines. they were at the natty peak and did full body 3x/week, often doing 9 sets to failure per muscle group (though usually with super short rest periods)