Really? A captain would rather you went straight to cards than get him involved to try and calm his player down?So summed up, its not a fair and consistent approach. It depends on who the captain is, their attitude and their nature, therefore, its not textbook good practise to approach captain, in short, it depends....
Its a variable. The captain has no special powers, at all, with regards the referee.
If anything the captain as per LOTG has some responsibility for the team.
if a captain cant see that, blue 5 is over stepping the mark, or cant tell that blue 8 is going to be dismissed for their next foul, then, that's their own problem. I know in Scotland, even from playing, if a ref called the captains in, the players would say "hey, its your job to control/manage the game".
It's entirely down to the referee how he chooses to manage the game - and as other have said, the stepped approach including the captains at "step 3" is considered a very good way of doing things in England (where the majority of posters on this forum referee). That doesn't mean it's right for every situation, but it's a tool that we're encouraged to use if the context allows it.