The speed of the projectile is ridiculous - particularly when compared to how fast the spinfuser fires (aka much slower).
The traditional plasma was a slower firing, very strong projectile weapon - but a fairly large projectile which made it awesome indoors for either assaulting an enemy base or protecting your own. You could fire big blobs of plasma in the enemies general direction and profit.
This new one is a super fast firing projectile that is just downright nasty. I'm all for new weapons going in, but each and every time it's affecting the overall balance.