I find that RPG combat tends to work best with at least 3 resources (and generally no more than 5 resources), with HP, MP, TP, SP, Cooldowns, ATB meter, Limit Break meter, and so on all counting as resources. (The exception is Action Battle Systems, where it can work well with as few as one resource, HP.) Having at least 3 resources enables a lot of Incomparables, interesting tradeoffs, and differing priorities and different points within a battle. So with that in mind, I might ask - what resources will Physical Combat-types use if they're not using MP? If there are other systems that gate their skill usage or give them interesting gameplay on their own, you can probably get rid of MP for those types (just be sure there's not a huge divide between the resource-neediness of mages and the resourceless, always-consistent nature of physical-types). If you don't have any of that, I wouldn't recommend removing MP from physical-types "just because MP doesn't make sense for them".