Assuming you've only changed the cartridge on both tables on one system and then tried the same on the other system - without introducing other factors, then you have reached the correct conclusion. That is: All other things being equal, there is a specific difference between one cartridge over the other. Or is it? Could the MC amp in one be impacting the performance? Yes. So the best you can hope to say is that in your rigs, the MM sounds better on rock.
Any truth to my feeling that MM carts are possibly better than MC on rock recordings?
I have an Ortofon Red on a Project Debut Carbon and a EAT C Sharp with an MC Ortofon Quintet Black. I have two systems and I've switched the tables between the systems and tried a few different scenarios and I hear a little more punch with the Ortofon Red. I know all things aren't equal here but I'm trying to explain this somehow. One system is Dynaudio Evidence Temptations with JC 1 Monos and JC 2BP Pre. PS Audio Stellar phono or a little Project MM phono. The other system is PrimaLuna 400 Evo Integrated with same phono stages and Salk Sound 3 speakers. The Project and Ortofon Red sound great to my ears. More punch and solidity of sound.