While this looks good on Scum Kath, I think both Dengar and K4 are going to be better options. people already want to stay out of her rear arc and adding two points to further incentivize that means you're simply adding two points to your Firespray for two abilities that will get used less and aren't worth the affect they have on opponent's flying.
The entire point of Kath is to use her rear arc, by this logic no one should use Kath in the first place.
Yes, using Kath's rear arc is the point of using her just like arc-dodging is the point of using aces. There will be quite a few situations when you won't be able to do either though. For example it's extremely difficult to use Kath's rear arc in the initial engagement as you kinda fly towards the enemy and the enemy flies towards you... The point is that Dengar and K4 both provide effects that are very competitive with Tail Gunner and they work whether you can fire using your rear arc or not.
All of this is mostly academic though. Ever since U-boats showed up Firesprays stopped being competitive (scum Firesprays that is, imperial ones never were competitive in the first place). Kath will be lucky to use her rear arc once before getting torpedoed to death.