Any truth to my feeling that MM carts are possibly better than MC on rock recordings?

Every cartridge designed for all genres of music, the rest is personal preferences.
As @zavato posted mastering engineers (disk cutting) are using MM because of their neutrality. I must admit that Doug Sax choice was the 881 stereohedron tip (not 681 elliptical ) from Stanton in the 80’s.
Regarding the lowest moving mass people should look for MI , but Technics made fairly low moving mass MM too. And not only Technics with its superlight Boron Pipe cantilever.

 I stand corrected- an 881! Thanks Chakster. 

I am in the initial stage of comparison of MM to my 1st new MC for various types of music.

I get instant comparisons from my single TT with 3 arms/cartridges to identical system via SUT with 3 inputs and Pass for MM.

shown in photo in my eBay listing of an LP I'm selling

https://www.ebay.com/itm/BAD-COMPANY-Vinyl-LP/133587830551

To properly proceed, I need to pinpoint volume differences, adjust volume precisely before switching, then listen to very familiar music.

What, if anything, does my MM Shure V15VxMR body with Jico SAS on boron do better than my new MC AT33PTG/II Microline on aluminum? Then, swap in the MM AT440ml I now use in my office, nearly new OEM Microline on aluminum, find the precise volume difference, now what?

I am buying new LP’s of worn LP favorites, and new LP’s of favorite CD’s, and new LP’s with superb engineering, some I learn about here.

So far, I am finding the MC to have everything and more than the MM, and find this particular MC’s superior separation and tighter channel balance giving more enjoyable imaging. That is also true between the two MM, the AT’s imaging just slightly better than the Shure’s, although I prefer the Shure’s brush feature in the main system to catch air borne dust just in time.

There’s also the MM Shure 97xe, elliptical on aluminum to compare, it might have some punch, or apparent punch, because of it’s different positioning in the grooves, who knows.

dunno

generalities as such are useless

No.