I still feel like there is a mistake, or more to this. Polearm proficiency is useless. Classes that might make good use from polearms already get the proficiency. Classes that don't get a polearm proficiency aren't improved by having it.
A couple of possibilities: 1) Fextralife misunderstood, and humans can actually choose a weapon proficiency from a list (and the list happened to default to polearm)
2) Fextralife misunderstood, and humans get expertise (double proficiency) in polearms
3) Larian has Homebrewed Polearms (or just Q-staffs) to add finesse to them.
Or there is some other unknown factor that makes this make sense.
Its undoubtedly good for blade locks and if there is something like a human only myrkul scythe that let's you use casting modifiers for damage every human caster could use it.
There'll probably be a gythyanki only sword for gish builds too id assume
