it's a shame strapping a bat to the downtube is a bit inconvenient.

you think this altercation deserves a death?

Doubt he's saying that about this particular incident. Had the driver started pointing a gun at the cyclists, then I believe it's justified to defend your life with your gun. You use your best judgement and hope the court favors your story if you do kill someone. Also, a bat is considered a deadly weapon. One strike to the temple and you're dead.

I wonder the legality of "detaining" this man with some amount of necessary force in order to keep him from fleeing the scene.

In hindsight it would have been smart to steal the keys out of the truck, especially if they suspected the man had been drinking, but either way, better for the cops to see the man in his "aggravated" state rather than at home with time to think about his story.

I think what he is suggesting is that a large adult male is capable of inflicting grave bodily harm when using a baseball bat as a weapon. I'm confident that in nearly every jurisdiction lethal force is justified in such a situation both legally and morally. I do not see him saying shoot the perp. I also do not see him saying shoot to kill. In fact I'll hazard a guess that the OP also knows that he if forced to shoot is only shooting to stop the assault.

Although I understand the behavior of the cyclists I also think it will hurt them in the end, or at least not help them.

Come on man...