the games that were supposedly amazing graphically ran like ass as they pushed the PS3 far too hard.
TLoU had constant FPS drops the moment any transparencies were on screen, Killzone 2 has insane input lag due to the GPU being pushed too hard (the main reason KZ3 had a significant graphics downgrade), and even after a full generation of devs developing for the PS3, the 360 versions still looked or ran better in 99% of games.
even Halo 4 beats all PS3 games on a technical level easily. solid 30fps, clean AA, low input lag, and visuals that people still bring up in your typical "this is what games looked like 2 generations ago btw." posts on twitter to mock modern graphics/performance.
The PS3 was clearly less powerful. the Cell SPEs helped, but only so far that it could be on par in some games.
the Cell had to make up for both, a lack of GPU performance and 4 missing PPE threads compared to the 360.
and then there was the RAM dilemma, where devs had to jump through hoops to use it efficiently, even an issue for Sony, who were unable to implement a system wide party chat feature due to the memory allocation issues.