To me, this question is leaning more towards "is x renderer worth learning?" because the "Vray vs MR" threads usually end up people attacking other people personal choices and that's what it really comes down to -- personal choice.

There are people who work easily with MR for Maya and have developed custom tools/workflows over the years and the hurdles have all but disappeared. Some people can't be bothered with lack of user friendliness in the MR implementation and they look elsewhere. Both are "powerful", I guess you just have to find your own comfort zone.