What I dont understand is why a mastery point is locked behind the achievement?
As most people already pointed out you dont need it to max the masteries. So why is it there?
Imagine someone grinding all 16 weapons, you surely won't do it for the mastery point. Neither will you spend 1000s of gold for a mastery point. You'll do it to get the skins.
So again, why is there a mastery point locked behind the achievement?
I tell you why: Because ANet knows some people have an urge to keep the achievement tabs clean.
It's a cheesy way of teasing their players.