To a certain extent I agree with 411A about a single-pilot Kingair driver showing a high degree of skill.
However, Multi-Crew Cooperation is also a set of learned skills. Loads of standard calls, more CRM, the division of who does what when, etc. etc. That the aircraft is relatively simple is not important. Someone who has flown it multi-crew has demonstrated that he has experience of working with another pilot next to him.
I went into the 757 course having never done any of that. As a result, the learning curve was a lot steeper than it otherwise might have been, and for someone on a first job on major machinery that slight levelling of the curve could make all the difference. Airlines want to hire people they know will make the grade, so every little bit helps.
An MCC course can only go so far.