There's a converse element to this also, though, which parents sometimes overlook: as kids mature, there will be obvious and somewhat durable genetic differences in height, size, strength, etc. While it's accurate that early-developing kids are often placed on higher-level teams and given a durable advantage because of that (as they get better training, competition, etc.), some of those kids might also just end up being bigger, faster, etc. (which can make up for some other deficiencies, in terms of overall effectiveness in play).
I presume the clubs know this also (explicitly or implicitly), and at least some of that "unfair" advancement of early developing kids is aimed to pre select kids who might be just bigger and faster generally, for better effective training. While this might disadvantage some late developing kids, it might also be selecting for the best overall potential, statistically (for a much more limited amount of access and resources available for soccer training). I'm not sure if that's accurate or not, but it seems like something to at least consider also.