Quicktime is a heck of a lot more universal than MXF or Cineform ever were.
That is precisely the problem. As a multimedia framework that needs to be installed and get's updated, QuickTime is buggy and flawed. As purely a container specification that needs to installation or updating, MXF just works.
As for Cineform vs ProRes, I'd not argue against ProRes in the MXF container, as long as I write the files for free on a Windows system without installing QuickTime. But since that's not possible (or likely) the alternative is Cineform in the MXF container.
It's just better.
