That is not how safety margins work. Safety margins are meant to give a buffer for unforeseen circumstances, they are not a ticket to just cheat. With this logic... why stop at a 25A breaker (30 in the US)? Why not just plug a 20A device into a 100A breaker, or no breaker at all?
No safety margin can account for purposeful circumvention, which is what connecting a 15/20A outlet to a 30A circuit is.
No safety margin can account for purposeful circumvention, which is what connecting a 15/20A outlet to a 30A circuit is.