Arnold did 20+ sets, jus saying. Yea yea yea he had good genetics but I believe there are people on this site that if they ran primo and dbol all year long they would look like Arnold. Maybe not but still fuckin jacked!
I just giot a routine suggested to me that is 20+ sets for each muscle group. sometimes 30 sets, what if you were on cycle?
To the OP, there is no magic number. Basically do what you feel is good and gets you pumped, its more important to be consistent. If in a couple months you arent seeing gains, and your diet is good, then try switching it up.
For instance, i do not train a lot of sets. Maybe 15 sets top for a bodypart, and that is a lot to me. However my buddy swears by 20+ sets for each bodypart. Hes big no doubt, juiced to the gills, but basically everyones different. Im just as strong as him and he lifts 2x as long as me. I have learned from my body that doing 15 sets is enough.