Biebs is half his age (25 vs. 56) and Cruise is probably even smaller than he is. They are both part of cults. Neither have a lick of experience. It makes no sense from any perspective. Let's do it.
From what I read the Biebs is taller than Jack Reacher, but Ethan Hunt has like 20 pounds on Justin. I think even at his age Cruise could take him. If Cruise is unwilling to do the fight they should get the dude from Arrow to get in there with Justin.