It's true. PS3 shines in exclusive games but a lot of multiplatform games run better on the 360. There's a long laundry list of well documented examples. Skyrim and Marvel vs Capcom 3 are pretty obvious ones. The primary reason is the PS3's sub optimal ram allocation and slightly less powerful GPU. I find it pretty crazy that console fans can get mad if someone says one piece of hardware is higher performing than the box they bought.
How powerful computer hardware is is a known value. It isn't some emotional thing that is subject to what fans want. It doesn't make you less of a person for having bought a PS3 and it doesn't make the PS3 a bad console. The PS4 is more powerful than the Xbox One, the Radeon 7970GE is more powerful than the Geforce GTX 680, the i7 4770k is more powerful than the FX8350. None of these statements should trigger an emotional response in anyone.