Differences in WvW and PvP builds?
i’ll let others provide a more comprehensive answer but quick one is for Conquest (pvp) its all about capping and holding points which means people are forced to fight on or very near the points. This makes AOE weapons like Longbow (its burst skill fire field plus might stacking from #3 LB skill) very very effective. For WvW its more a mobility thing, using terrain and line of sight. There is no requirement to fight in a particular area and so you can “roam” around and move as much as you like to engage and disengage from combat. This makes GS/Hammer a much better setup for WvW.
“Buff my main class, nerf everything else. "
It’s mainly the stats: you have access to stat combos in WvW that aren’t in PvP such as Dire for instance. Possible damage output is also higher, consumables create further imbalance. WvW is a place of powercreep.
Then there’s the fact that WvW roaming is more like Practice mode in PvP, there are many bad players running bad builds, that’s why there’s even more “diversity” (and many refuse to change build/gear when going into WvW from PvE because that costs gold).
longbow in PvP is key because, in combination with the defensive trait Cleansing Ire, it allows you to remove up to three conditions at once with the burst skill. the other weapon burst skills are unreliable because they require a hit to trigger Cleansing Ire. longbow is also good for utility: it has immobilize, blind, condition damage (burning) and the burst skill is nice for area denial.