[@Savato]
I never intended to start an argument, and hope I haven't done anything as such.

As this is a grey area with limited information, I think the only logical decision is to allow the controlling player (you) to decide the exact statistics of these weaponry. I would ask that you decide what the projectile speed of plasma weaponry is, at which point we would have a consistent basis for situations like this.

Plasma weapons, at least in the game, have no increase to accuracy. The only things I can think of are that laser and plasma weapons are longer range in the rifle weapon type (but nowhere else) and that plasma snipers have a higher crit chance.

Personally, it seems unlikely to me that the Mutons would have been able to pull off the shot. Average human reaction time is 270 milliseconds. That's for a simply click on the screen, ignoring aim. Mutons most likely have massively superior reflexes and perception, but hitting Doomsday at sonic speeds is like trying to shoot a bullet out of the air. They would need to compensate for speed and drop on the aim in 5/100ths of a second.

If you want, I can edit my post. I'll leave the decision up to you.