I wouldn't recommend this method for the Schumann concerto... it needs to breathe! MIDI is so suffocating -- might work for early classical period concertos, though.
Same argument can be made for the MMO recodings. There is no communication between the conductor on the recording and you as the soloist. There would be breathing, but it wouldn't be
your breathing. Either way you would not be practicing the essential skills of communication with the conductor.
If you wanted to, you could program your own rubato and breath into the MIDI. But that takes quite a bit if fiddling.
I'd say using either method would be OK as long as you understand you would not be practicing details of your breathing, phrasing, etc. It would be good for learning thematic elements that involve dialog between the piano and orchestra, and when the piano has lead or is subservient to the orch. As long as you know how to fill in the missing breath, phrasing, elasticity, communication when you meet with the conductor.
I would treat it as practicing elements of the piece, not practicing a performance of the piece as a whole. Just like slow practice of technical parts, or fast practice of lyrical parts, or singing out melodic lines, etc.