Forgive my lack of knowledge, but what does a midlength offer that a carbine doesnt? Does it run better or have any major advantages?
Longer direct gas systems are less violent and easier on the weapon. Shorter direct gas systems are more violent and harder on the weapon. This is why carbine direct gas systems wear out parts faster and need heaver buffers, stronger extractor springs, etc…
Check out this thread on mid-length ARs and associated threads/links here
https://www.m4carbine.net/showthread.php?t=13581&highlight=Midlength