That's not the only reason, though. The bigger leagues are much tougher for the players as well as the managers and at board level. Being kicked up and down by Watford isn't exactly the best way to build a young player's skillset, whether we're talking mentally, physically, or technically. Going up against Valencia and Sevilla as a young Barca prospect is not the same as being a big talent in an Ajax team facing Groningen or Vitesse.
If the Dutch league were richer and tougher, Ajax would be an entirely different team.
It's also worth noting that their success in Europe is an outlier, not some kind of masterminded effort. Exception proves the rule and all that.
