yea ive heard two theories about DOMS, both from what i thought were credibile sources (and may be, just with different clinical findings): 1. microtrauma/tears of the sarcomere and 2. lactic acid build up
i agree, i think a person should train at a pace where they can make a net strength/size gain over a lengthy period, say 6-8 weeks. If it doesnt happen, they should consider altering a number of factors like intensity, frequency, volume, rest/sleep, diet and adjust accordingly..
to the OP, youll just have to use trial and error bro. If youre not getting stronger or bigger (gains will come more slower the more advanced you are because youre farther away from homeostasis and closer to your genetic limit), then somethin in your plan needs to be tweaked
its taken me 2+ years to find out what works and im still not sure if its the most optimal