But the Sharpshooter is not better than non-specialised fighters.
Precise Shot sacrifices damage for negating cover penalties. This is important for archers, but melee fighters generally don't have the same issues with cover that archers do.
Shift is not archery specific, and Snap Shot is simply the archery version of Jab, to which other fighters have access. Furthermore, Shift and Snap Shot/Jab are situational bonuses - Shift is taking a modest damage hit in order to get a modest amount of movement, and Snap Shot/Jab is taking a major damage hit in order to get a large amount of movement. Neither is simply a power-up, and a fighter who had access to neither of them would be less mobile in combat, but not necessarily less mechanically effective as a fighter for that reason - for example, s/he could be very sticky and/or charge-y instead, negating the need for the mobility that Snap Shot, Jab and Shift open up.
Ah, but it can still be called a "weapon specialization" because Snap Shot and Precise Shot are specifically made to work with ranged weapons. They make you more versatile and effective with ranged weapons in situations where you might not otherwise have those options-but only if you're using a ranged weapon! If you're using a melee weapon, you've given up two maneuver slots for effects that don't help you. So going by the definitions I've heard in this thread, it's still a form of weapon specialization.