It would be a better and a fair fight if the HQ was less exposed and the cops had respawn timer. It is not a matter of having skills to kill the waves of cops, its the fact that does not make it fun.
The fact that kavala hq is very easy to attack is bad thing.
Yesturday, for example, my friend killed 4 cops in kavala hq with an SDAR. He wiped the entire HQ in 20 seconds. He grabbed me and started heading towards the gate to save me when a cop that was killed first spawned right behind him and downed him. Is that fair? where is the fun in that.