If he manages to defeat a single league, he still can't be considered a master. He has many other tasks to complete, such as going back to other regions for the sake of having other accomplishments. I mean, beating the Unova League, if he even does that, just leaves, uhh, I dunno, maybe 4 other regions+ whatever Regions come next+ whatever else the series left open, like the his Charizard being weaker than the other Charizards in Charizard Valley, his ping-pong Ambipom, maybe a run-in with something he released like Butterfree or Lapras? And then there are other events that we don't get in games but exist in the anime, like the air master championship, Ambipom's ping-pong, etc.
He will live on, even after anyone wants him around
He will live on, even after anyone wants him around