Which of the last 10 winners hasn't won it on merit then? Ronaldo last year? Messi the years before him?
My opinion for recent times:
Iniesta in 2009 (CL semi-final clutch goal and final performance, generally awesome that season).
Xavi in 2010 (one of the performances of the season across all leagues, sealing the league title in the Bernabeu with 2 superb assists, completely dominating the game, World Cup win, generally awesome that season).
Messi in 2011 (CL semi-final solo goal and final performance, generally awesome that season).
Ronaldo in 2012 (sealed the league title in Camp Nou, scored against every opponent, semi-finals in the Euros, probably his best ever season, Messi stole it from him with his ridiculous goalscoring form towards the end of the year when he broke the all-time goalscoring record but ultimately he didn't win anything but a Copa del Rey).
Messi in 2013 (Ronaldo stole it from him with that WC qualifier hype towards the end of the year during the voting time while Messi was injured but remember that Messi was a 1 man show the entire season, scoring against every single opponent and
consecutively, 46 goals in 34 games, without injuries he was on course of breaking his own La Liga goalscoring record (50) once again, making sure Barca won the league with 100 points, coming on with 1 leg and making sure Barca qualified for CL semis against PSG, whereas Ronaldo got knocked out and sent off in the Copa final and Madrid generally bottled the league by December).
Obviously those who actually ended up winning (Messi and Ronaldo) also had their arguments and it's not as if Heskey won it but yeah, that's my opinion.