I’ve recently gotten back into this game and run into a few troubles that a Google search wasn’t able to solve. First-if I switch an orc from being my bodyguard to a mission, will that possibly lead to their defection down the road? And I’ve run into Captains who far out-level me-is that common? Did I go somewhere ahead of schedule?
I’m not sure what the answer is to your first question. It seemed to me that having recruited orcs defect was more or less random, possibly increasing when you have a lot of recruited orcs.
Yes, it’s common to see captains that out-level you, especially in the beginning phases of the game (e.g. up to level 20). It can be frustrating when you’re trying to recruit orcs for your first few castle assaults; you might need to shame an orc a few times before being able to recruit them (which I found a bit tedious).
It’s more trying to kill the out-leveled ones, really. And of course every time they get stronger when they kill me. sigh
On the bright side, it’s easy enough to run away from most enemies, especially once you unlock your elf running ability. But it’s still a bit of a slog until you unlock really powerful abilities (like summoning a graug mount) and then you start breezing through most fights.
I’ve also accidentally had one of the orc singers get killed. I wanted to keep 'em. 
I did some googling on orc betrayals and it sounds like the betrayal chance is higher than normal at the beginning of the game. Also there are some things that greatly increase the chance of betrayal, like attacking your follower’s blood brother or hitting your follower with too much friendly fire.