The kVA of AHF is as you rightly pointed out = Losses + VxI.
But, the point is, what ever the harmonic current injected by AHF is used to cancel out the harmonic current from Non-linear loads (VFDs, DC Drives, Furnace, UPS, Etc). Hence as seen from system side, the net current will be the vector difference of Load harmonics and Active filter harmonic current.
It is like Capacitor connected to motor.
The capacitor will draw leading current & the motor will draw lagging current. The Capacitor current & motor inductive current will cancel out vectorially, and as seen from the source side the effective current will reduce, and hence the kVA will be less.
Active Filter topology is similar to above.