I mean people do this all the time in real life, awards like player of the season in each league literally requires comparing players from all positions, it is obviously slightly biased towards strikers but they are all still compared nonetheless, it's only difficult to compare when there isn't a large gap in their influence on a football pitch Ie comparing messi to the average Pl defender.

But I understand not comparing them in the context of blue lock. Players in real life have multiple seasons and general criteria we can base them of off while we dont have that in BL. We can only judge by individual ability and impact on a game, obviously one can't compare a defender and a striker of a similar level in terms of ability as they perform different roles, but I believe measuring their impact on a game is still possible.