They are twice the size though, and the 'core crew' usually means they have enough to leave the harbour, not actually do anything useful. They will still need more jetty space and increased maintenance, espcecially if they come with helo capabilities (for helos we also don't have, and would have their own flight crews etc which we...also don't have).
The MCDVs are being crewed by reg force now, which is making the crew problem on the heavies worse.
In the short term, if we tie up some MCDVs and mothball a few CPFs we might have enough people to actually sail the ships we have safely and be able to do enough maintenance to have them up to the safety standard for basic sailing.