But yeah, I agree. The WA2000 kills in one shot anywhere from the chest up without stopping power, meaning you get to use the amazing CB Pro instead. No aim assist when people look at you is pretty cool.
The M21 will only kill in in one shot to the head and neck without stopping power, so in order to get easier one-shots, stopping power is a must, unlike the WA200. One advantage the M21 has over it is the larger clip size. The M21's 10 to the WA2000's 6. They also have similar recoil, but the M21 clearly has less.
It's clear that unsilenced, the WA2000 > M21 EBR
When silenced, it's pretty much the same story, if not a stronger argument for the WA2000. The WA2000 has a 1.5x multiplier to the chest, meaning that with stopping power, the WA2000 will kill in one shot anywhere from the chest up.
The M21 is a horrible sniper when silenced. Even with stopping power, it will only kill in one shot to the head or neck. I guess it's ok without stopping power as a two shot sniper, but it's pretty crappy. Nobody wants a two-hit kill on a sniper.
In all honesty, the WA2000 is undoubtedly the best silenced sniper in the game, because it has significantly less recoil than the .50 Cal or Intervention, but still outputs the same results.