I would say that most MX's did not see professional use. Nikon was the top 35mm pro camera, with Canon catching much of the rest. Minolta had their pro level interchangeable finder machine also.
I would say Olympus took a lot of the compact pro camera market. The OM-1 and MX sold mostly to the amateur market, despite being pro-spec. and having their own systems. They cost the same or less than the Nikkormat and FM series, putting them into the amateur price range. Olympus' system was more extensive, and excellent though Pentax was, they didn't make the same run at Nikon's and Canon's extensive lens lineup that Olympus did.