What means one more year under Valverde? It means another year of playing gala XI, while failing miserably because of the tactics, the mental block, age of the players, stamina issues in the last month and Messidependencia.
Next year, it will still be somewhat easy for us domestically, since RM will still be rebuilding IMO. But, we have no chance in Europe. But after that, when our seniors are really seniors, when Ernie leaves, we have no new blood at the club and Real Madrid are back to being a force fully integrated in 2020/2021 season.
Last great years of Leo should be used to keep a certain level of results (well, he can basically win Liga on his own + MATS, as shown this year), while rebuilding the team around him, not to play the seniors (Messi's friends) each game and benching every new signing with the exception of Copa game here or there.