Level 20 Berserker (levelled well), fully equipped. T2 purge - prisoner wave. While I’m one-shotting my way through the wave, he stood behind doing nothing. One prisoner slipped past. I killed the next 2, then a second got past. I killed the rest of the wave, then turned and killed the two that were attacking the thrall. In the approx 10 seconds they had been there, he had lost 1/3 hp. If they don’t fight back, they take a lot of damage fast. (And that’s not accounting for the possibility of people teleporting to a location and heading into combat without noticing that their thrall took some ridiculous amount of ‘fall’ damage from the teleport, so is in a weakened state - separate bug, and arguably people should take the time to notice, but it’s going to happen a lot right now.)
Beyond that, there’s also the simple point that I was arguing against your initial statement - which was to tell someone they should get the top thralls, when they had already stated that those were the thralls they had.