I would like you to give an example prior to the Rolling Stones catalog where the drums and bass are as loud and as up-front as "Rain" and "Tomorrow Never Knows".
Im thinking Satisfaction and 19th Nervous Breakdown for two, both 65 where you could hear prominant bass (but maybe Paul insisted on it being even more prominant for Rain)
Of course Abbey Road is closer to prog than Sgt. Peppers its more than two years older than Sgt. Pepper so you would think they progressed
Thats what I dont agree with, by 1969, King Crimson had released the first full blown prog album (in the Court) so the genre was established and Abbey Rd was more 'Rock' than 'Prog Rock', although parts of it were Symphonic and Arty..
Pepper was Art Rock, sometimes referred to as Proto Prog, but it was more Prog than Abbey Rd IMO, because, first of all it was a concept album with gatefold 'artistic' cover art, it had prog elements (think the intro to Fixing A Hole) songs with differing time signatures (Mr Kite, Day In The Life), a large variety of instrumentation, mellotron, sitars, Indian percussive instruments, full symphony orchestra etc