Considering Archer is a dps role, I assume I should focus on STR right? But I've seen several topics saying DEX, but why? That seemed to increase in its own for me in the beta as I dumped everything into STR and still my DEX was the highest stat, what does DEX do anyway? Affect evasion/accuracy?
Dexterity could be the least or most important stat for Archer depending on several factors. If your primary concern is only instanced content where accuracy is 100%, then Dexterity is probably the worst stat to invest in as an Archer. First of all, DEX appears to have almost no influence on Heavy Shot damage, and has a marginally better return than STR on Light Shot damage. Also, there appears to be some sort of “cap” on Dexterity. After reaching a threshold of 280 Dexterity, adding any more dexterity (up to 325 in my data collection) appeared to add no damage whatsoever to Light Shot or Heavy Shot. However, it should be noted that I experienced a relatively higher accuracy with high Dex gear, so if your focus is on out-of-instance content, then DEX may still be a viable option for stat focus.
The second link is out of date. You can tell since they mentioned ammo which is no longer in game. The first one even says DEX.
ARR changed stats. STR is now melee damage not all damage, DEX is ranged damage not accuracy. For accuracy they combined magic, melee and ranged into one stat that is simply accuracy and found on gear and materia.