I like M1A, although after starting to pin, I feel oral only cycles are honestly a waste. Sure, you will pack on some decent mass. But as soon you get off those gains dissipate very fast. Then your left with crushed Test levels with very minimal gains. At least in MY experience. This would happened to me even with a solid serm based PCT. Heck, you may run those orals and keep 90% of the gains. Who knows.
IMO the % of the gains that most orals supply is heavily slanted towards glycogen supercompensation and water in the muscle. It looks awesome for sure but there is simply no way the human body is manufacturing 10lbs of actual contractile tissue in two weeks lol, I wish. With inj. gains are "slower" but in reality they are likely progressing at the same rate as orals minus the water/glycogen.
OP the muscle you retained from SD, if it was significant, leads me to believe that was tissue that was still below your natural limit. Say natty you would top out at 200lbs and you ran SD at 180 and got up to 200. The body will hold that better, assuming training/nutrition is still on point, than it will when you push from 200-220. I have nothing to prove this scientifically other than having seen it play out time and time again over the last 20+ years.
Overall I don't think the actual muscle tissue from orals is "less permanent" than inj's. IMO the issue lies with not being able to stay on them long enough to solidify the new tissue.