I don't see why people assume medichlorian manip is exempt from Mace's superconducting loop. It's a force power, and it's power that is indiscriminately being circled between Mace and his opponent.
It's also not exactly going to be easy for Plagy to pull off medichlorian manip in a heated lightsaber duel.
Mace with or wihout vapaad has plenty of evidence suggesting he's close to ROTS Sidious which is suffecient to make him a signifcantly superior as combantant toP Plagy. I'd imagine being signifcantly better would be the biggest factor in this fight.