I run Mono M4s, XT (older 2 piston with no servo wave) and old style Minis on my bikes, and I've used Mono Minis on hire bikes for a couple of weeks in the Pyrenees, all with 180mm or thereabouts rotors. I weigh about 100kg in bike mode.
They're all plenty powerful enough, they've all got good modulation, they're all perfectly good brakes.
I'd say that if you're experiencing a lack of power from your Mono Minis then they're either not set up properly, they need a bleed or your pads/and or rotors are contaminated. Or the pads are a rubbish compound.