Honestly? Are you even trying to attempt attach "realism" to MW2? It's an arcade shooter dressed up in some HIGH SPEED LOW DRAG GO LOUD DROP TANGO SUPPORT. While some of the weapons resemble their real-life counter parts, the weapon stats are just goddamned confusing. For instance, despite the fact that TAR-21 and M4A1, FAMAS, L86, and MG4, M16, ACR, and F2000 all fire the same 5.56x45mm NATO cartridge, their damage is completely inconsistent. The TAR-21, FAmAS, M16, and L86(40) all deal more damage (40-30) than the M4A1, MG4(30), ACR, and F2000 (30-20). The first set also deal more damage than the M240B (30), which fires the much more badass 7.62x51mm NATO. The SCAR-H fires this and does 40-30, and the FAL fires it and does 55-35. I won't go into detail, but also consider the UMP-45 and the Vector. Both fire .45 ACP, yet the UMP does 40-35, and the Vector does 25-20. Where's the sense and realism in that?
(By the way, the guy with one arm is dead since COD4.
Anyway, the more important factor, which, this article more or less addresses, is that they are two completely styles of FPS. Comparing MW2 and BC2 is like comparing apples and carrots. It's just goddamned illogical and stupid.