The Mikrokosmos is music. Bartok was a brilliant composer and teacher. A lot of beginners books are just mechanical studies. As a student you shouldn't be limited to playing only the Mikrokosmos any more than you should only eat ice cream and nothing else. I studied from the Mikrokosmos in my lessons but I also was assigned a lot of other kinds of music (Bach, Mozart, etc). Variety is important for a lot of reasons.
I still love Bartok's music, especially the"String Quartets", "Music for Strings, Percussion and Celeste", the "Concerto for Orchestra", "Sonata for Two Pianos and Percussion" and the "Divertimento for String Orchestra" to name some of his music. These works are of very high quality and offer much to any careful listener.