I disagree with that. I don't care if the PK offense is 5m out or 20m out if you get the ball into goal you have gained all the distance and tactical advantage possible.
You've gained all the territorial advantage possible, yes, but that might not be enough territory. If you're playing penalty advantage for an offense on half way, you're not going to say there was advantage gained if the team could have a scrum 5m into their opponents' half, so why apply a different criterion near the goal line?
If you have a maul from a lineout 5m out, a defender comes in from the side, play advantage, the maul goes over the goal line and the ball is held up are you really not going to go back for the penalty? I've never seen anyone do that before.
In a more extreme scenario: blue are two points down in injury time, red offend 5m out in front of the posts. Would you immediately blow up for the penalty? After all, blue could get over the goal line and knock on trying to ground the ball.
N.B. I can think of a case in an international where the ref was playing penalty advantage to white (close to the goal line), they were held up in in goal and he ended the game there. It came up in a society meeting and the conclusion was that it was very much a f*** up.