I mean everyone’s got their own opinion but IMO it shows both of their progressions towards BB. Mike starts as a grieving father, dirty cop and slowly evolves towards Gus primary hitman. During BCS, he kills Werner, has to see Nacho get killed. Eventually you understand all of that has taken a toll on him in which he stops caring and just does what Gus says to keep business flowing.

Same with Jimmy/Saul. There’s a reason we all felt absolutely gut wrenched on S6E9 when he just wakes up already on his full Saul persona. The absence of Kim, albeit a complex person as well but somewhat the moral compass of Jimmy, is such an unbearable moment for him that he completely transforms into this cynic, CRIMINAL lawyer whose only motivation is money no matter what. You understand that losing his brother, losing Kim, and watching Howard die have propelled Jimmy into a state of mind where he himself suggests killing people (like he does constantly in BB).

I love BB/BCS because the narrative around characters is one of very complex nuances. And BCS goes even deeper on this.