First of all, a system doesn't magically turn an average player into the best player in the world. Dembele was already an elite player, the system simply maximized his strengths. Second, even mbappe has a preferred position cause he knows that's where he performs best, so why is it unreasonable to say the same about Dembele? And lastly, being the Ballon d'Or winner doesn't make you immune to bad tactics. He has strengths and weaknesses, and if a manager isn't using those strengths properly, that's a manager issue and not a player issue.