Around the 80s. The attitude that he was too powerful to be interesting had been festering throughout the 70s but the 80s saw a full blown pushback from all sides. The film franchise had crashed and burned, and in its place came the massive marketing and merchandise success of Batman '89, which would pave the way for Batman to dominate the 90s (even when the Batman films went downhill, they never got as bad as Superman's, plus there was the animated series). Comics saw a widespread industry shift thanks to works like Watchmen, The Dark Knight Returns, Crisis on Infinite Earth and *insert Marvel thing here* (this was the decade that saw Miller's and Nocenti's Daredevil, Claremont's X-Men, Dematteis and "Kraven's Last Hunt", Roger Stern's Spider-Man and Avengers, Jim Starlin and "The Death of Captain Marvel", and The Punisher's first solo series). Poor Superman drowned under this new creative wave, whether he was being interrogated by Watchmen, being made into a government stooge who gets his ass kicked in TDKR, or being made irrelevant by Marvel's push into darker, more serious storytelling. DC's reboot of the character in the wake of Crisis couldn't stop the fact that the comic industry as a whole seemed to be saying that Superman was old, outdated, and needed to be left behind.