Well, Wes did have the authority to order NCOs aboard the Enterprise... Mostly we see Officers on the Enterprise, and Wes wouldn't be able to order them around. We do see Acting Ensign Crusher order around his science team when they are assigned under him in the chain of command.First, I never got the impression that Wes' promotion included the ability to boss people around....Nog should have assumed command and ordered the Valiant back.
And the chain of command is where this leads... ASSUMING Watters had legit command of the Valiant, his authority came from a CAPTAIN. Where would Nog's authority to take command come from? IRL, if a Colonel gave an order to a 1st LT to assume command of a special ops squad as he was incapacitated, a Major could not show up and take the command from him without authority that is from within his chain of command OR superior to the Colonel. In the modern military, when an officer is given command, he is given command on the authority of the Flag officer that assigns him command and can not be relieved by someone that does not carry sufficient authorization to do so. So, Ensign Nog could have Watters salute, but he did not have the authority to assume command... And I doubt that Starfleet would allow an officer as low ranking as an Ensign general command abilities.