Another factor is that a lot of folks do not run large ships at all, nor ones that are very high point costs, so the BT/Avenger becomes expensive overkill. I've set up my very expensive ISD-I to kill a ship that is half or less than half its cost.
Add to that the likelihood of getting into range 1 of many of the smaller ship fleets and its a bit 'one trick pony'
Edited by Englishpete