Not sure about Mixcraft, but with Reaper... All set of existing modern VST MIDI processors should work and there is endless possibilities to create own when required.
I mean Sonar had CAL and MFX. Both so to say far from perfect at the framework level (may be that was ok 20 years ago) and long time not advanced.
For MIDI routing, I do not think there is something in Sonar which work better then in Reaper. Not forget about nasty clashing with Surfaces and Remote Control functionality in Sonar.
I can not say much about the editor yet. I have not found some "super features" recently added into Sonar and I have not managed to change note colors, but basic editing works and staff view (rather convenient to switch into) looks reasonable.
What exactly is "underwhelming"?
PS. In Reaper, almost everything is not intuitive at first. But even in default layout, once you learn where/what/how, it is possible to understand what is there, why it is there and how to operate it. It is logical. May be not with the logic particular person except, but logical. And finally, there is quite some flexibility in modifying things (instead of the claims "we have (re)defined it the way we think is better and you should adopt to that...").