yes, I agree the Lionfish doesn't forget his hunting. I have a small lionfish that eyes my little Picasso Trigger fish all the time. I have to keep a close eye on him. If it wasn't a trigger, I wouldn't have put the two together. If the lionfish keeps growing how he is, then I would definitely have to remove the small trigger fish.
Although I do have 2 convict damsels in my tank with this lionfish, he is again to small to eat them. When the lionfish grows a bit more, the damsels will be gone.
Do to the nature of a reef, having inverts, I would predict the lionfish would clean house.