10) X (a fullback) is better than Y (another fullback) just because he is better in attack
The biggest change in modern football has been the evolution of the role of fullbacks. With players getting fitter, faster and sturdier in all positions, these days, fullbacks are pushed forward on nearly every attack to provide more options to the midfielders and forwards. It is now a common sight in football to find a fullback running into the penalty area, delivering crosses and even taking shots on goal.
Yet, the primary role of a fullback is still to defend his goal in the maximum number of game situations to the best of his ability. Unless a fullback is able to fulfill his defensive duties, keep opponent wingers in check and track strikers’ runs, he is still not qualified enough to join in with his team’s attacks.
If necessary, he has to curb his attacking instincts, refuse to join attacks and keep the defensive shape of his team proper.
The role that fullbacks play in attack is auxiliary. The only time that the argument in question would be valid is when both X and Y are almost as good as each other in defence. If X is even slightly less disciplined than Y in defence, his extra utility to the team in attack does not make him a better fullback – many more goals may be conceded by the team due to a fullback’s positional indiscipline than they can hope for him to create in attack.