Deliberately sabotaging people does not require that the sabotaged person be under-performing or low quality. That’s the point. If a BR prevents you from hiring an unqualified person to be a sacrificial lamb, then you just hire a qualified person that can get past the BR to be a sacrificial lamb. The existence of BRs is absolutely not a foolproof check on this.

You might ask “why would an HM fire someone who is qualified to do the job?” The answer is that Amazon requires that someone must be fired. If you were an HM, who would you rather fire: an existing qualified tenured team member who already knows the ins-and-outs of your team and system, or a new qualified person who would require extensive training and time to get up to the level of the tenured employee? You’re going to pick the new person, even if they are qualified.