M4 has a select fire position, much more heat and stress from full auto fire than semi. I’ve yet to meet a person that can pull a trigger fast enough and LONG enough to bring a semi to the point of melting parts and failure. the hand will give out before that happens. and I have seen people try. even with a full you have to run many rounds and fast mag changes. Now the devices like bump stocks and binary triggers make it possible. I don’t think the m4 is any better than a well made AR. just my opinion. and opinions are like bungholes. everybody has one.
They are up there with BCM, DD, SOLGW etc. By mid range I mean general use with quality parts. Most of the spendy spendy stuff is precision oriented or piston driven. A regular DI built for general use shouldnt cost over 2k, imo. I wouldny spend over 1.5k.