OK, let's start with the assumption that MCC training is beneficial and important. Note, I'm not claiming that it actually *is* beneficial and important, just that whether it is or not is a completely separate question than the issue at hand.*
With me so far? OK presumably one learns things in an MCC course, good things, beneficial things, things which are important to learn. Why would one assume that one would learn those same things by flying a certain number of hours for some operator? What is the guarantee that the operator's procedures are good? Maybe they are bad, and a you've done for those 3000 hours is learn and practice doing things the wrong way?
*I'm sure that are people here who hold the opinion that an MCC course is a compete pointless waste of time, and I'm not disputing that. Perhaps it is. But that is completely irrelevant to the question of whether a certain number of hours of experience of unknown quality should be substituted for an MCC course. Obviously, if one believes it's a pointless waste of time, one believes that *no-one* should be required to take an MCC curse, but that train has already left the station, so that discussion is moot.