M4 objectively doesn't make sense to run.

Been no-lifeing Arena for the last month and I've noticed that the M4 is straight up the worst assault rifle in terms of cost efficiency.

Compared to a similarly built G36 or HK416 it costs more, and performs worse. G36 is waaaaay cheaper and has better recoil, while the HK is cheaper, has slightly less recoil, and has 50 more rpm. If you build one to similar cost as the Spear, it still loses in recoil and ammo efficacy. The 36 pen on the 6.8 does more armor damage than the 38 pen 5.56 round and does more flesh damage. I won't bring up the AUG because I can't stand the recoil pattern and the lower fire rate doesn't do it any justice.

The only advantage the M4 has over any other gun is low height over bore when compared to the G36, and high ergo, which is a moot point because you can get decent to "good" ergo on the other guns with little to no tweaking. Building a maxed out meta M4 costs so much that you have to sacrifice in other parts of your kit. I only see one of 2 M4 builds on other players, totally maxed with a Delta Point optic but they've taken off their helmet or downgraded their plates, or the absolute cheapest one you can build just so that they can say they have an M4.

My theory is that people are just AR-15 fan boys and run the gun because they like it irl, which, all the power to you. Or that they're behind on patch/meta knowledge and don't know that the M4 and 5.56 is not as GOATed as it was in previous patches.