I assumed that the player is unhappy not with the fact that there is no way to literally kill an enemy in the game, but with the fact that there is no normal combat mode when encountering slavers. That is, if the player encounters, for example, a Wild Cat or an Infected Scientist, he can control the process, use attack and defense alternately, resort to contextual attacks, use magic, and so on. But when encountering slavers, there is nothing like that - everything happens automatically, the player does not control anything. As a result, the player does not get the feeling that he just kicked the bastard's ass.
In addition, in normal combat mode, if you skillfully use combat control, you can defeat even such a strong opponent as Mistira, having a modest level of strength, nimble and resilience. When encountering slavers, you have to pre-increase these parameters, which requires multiple repetitions of the same actions and a significant amount of time.