Hmmm maybe. The more I think about it the more potential it has. Maybe among the thrall there are one or two bigger than average thrall that move slower but one shot you like light switch. For a boss maybe one that is like a "rat king", ten fused together or something and they call in swarms of thralls. As long as it's just not a regular thrall five times the size and is a bullet sponge, This could be a great idea.