I agree that outside backs shouldn't be captains - they're too far from the ref too much of the time. But I don't like half-backs and captains - they've got enough responsibility as it is, making decisions in the moment. Captaincy decisions are a different kettle of fish.
eg when the SH has the ball and there's a chance for a quick tap and go - he needs to be making that decision, unless his skipper is shoting at him not to - if he stops and second guesses himself, then it's already too late.
If a FH is wondering whether to go for the sticks or the corner, he might may need to hear both sides of the argument. Trying to second guess yourself only leads to confusion.
I like my captains to be in the back 5 of the pack. IC or hooker can also do it.