Dr Strange has plenty to distinguish himself from the other magic wielders. Virtually none of them have the same 70s psychedelic high fantasy stye. Stripping that away from him to turn him into a bad Buddhism cliche would be missing the point.
As for why his books have struggled for decades? I'm going to blame it on bad writing, or more precisely, repeatedly sticking writers on it who are unsuited for the title. Dr Strange is not an Avenger, he shouldn't *be* an Avengers, so if you keep having writers whose idea for any given character is "give them Avengers plots", your going to have issues.