Primordial Archer Ranger Build

Thinking of playing a human Primordial Archer Ranger in a Grim Hallow campaign. Grim Hallow Humans get bonus damage to creatures that have not yet gone in the initiative order and Primordial Archers get some abilities to boost damage as well.

DM likes standard array - so likely going for a Str 12, Dex 17, Con 14, Int 8, Wis 14, Cha 10.

Looking at Fey blessed for Background (magic initiate to get Shield) 

my question is would the Vex mastery on a short bow (d6) produce better damage overall than a long bow (d8) with the Slow mastery? I could sacrifice Con for Str and try and get Great Weapon Master to boost longbow damage, but I’m reluctant to take the hit to Con, but maybe as a distance Archer with access to the Shield spell the sacrifice would be worth it? 

Thoughts appreciated 

It depends the typical AC of what you're fighting.   The damage difference is 1 DPR per attack if the hit rate is average. But Vex adds an average +2 or +3 to hit, which is more valuable if you're fighting a lot of high AC monsters, and is better for piggy backing other on-hit type effects (like Hunter's mark).  Given that you get additive damage as a subclass ability, more consistent hits does more for you in overall combat than slightly higher weapon damage.   

Slow only gets more valuable if you're trying to keep something from approaching you from a distance.