In the Dad's Army episode, 'Room at the Bottom', we discover that Captain Mainwering is not a Captain at all, has no rank, and is demoted to Private. Out of the rest of the platoon, who do you think would have made the best commander if one of them had to be put in charge?
The only two, I see with any chance are Walker and Frazer. Walker would be very lax, but he's also the most competent of the lot. Frazer would be stricter, and from the snide comments he gives about Mainwering's plans, you can see that he'd probably come up With more sensible ideas. Wilson is far too mild mannered to make a leader.
I wasn't asking about changing the show; I was asking if Mainerwering had not been in command, who would have made the best leader. You're right that none of them are any good at leaders, but neither is Mainerwering, so it is just a bit of hypothetical fun.