As others have said, that depends on what you consider OP. The very first Superman stories in 1938 had him pretty much at Spider-Man levels of power, just with invulnerability to bullets added. Then, with the Post-Crisis reboot, his power was lowered from planet moving levels to being able to move a mountain, where it stayed for about 15 years before being ramped up again. That's the power-level for Superman I prefer. There are individual stories where he's depowered or starts at lower power levels, like Grant Morrison's Action run.