In most environments except hard desert conditions you could not get me to give up mine. Parts availability and continuity are outstanding. Accessories, general knowledge, it’s all there.
However, I will not go below the full 16" barrel. That is to say 16” not counting the flash suppressor. M-4 barrels are around 14" and that is the VERY bottom of the performance curve for the 556 / 223. Velocity is right about 2,400. The 16" barrel will rock in at around 3,100 fps.
Your mileage may vary…
+1. You'll also note the USMC does very little complaining about their new 20" M16A4's.
The M4's "problem" is barrel length, nothing more.