Thing with plasma, is you don't need that great strength or accuracy, whereas a decent CNC router table will be engineered for strength and accuracy.Comment about routers was they have to work with considerable side loads cutting, so wondered if the same CNC would be better with plasma.
The downside is strength and accuracy increase weight speed, which reduces speed and especially acceleration.
However a decent router table running servos, should be adequate for plasma, provided you're not trying to cut intricate shapes in thin sheet that really needs a sustained cutting speed for plasma.