You are pretty much right there is not a viable 5th major legacy for a DPS Weapon so I would use it as an Agility increase were I you, on the minor side of things I tend to take Surety of Death damage over time as its a pretty beefy DoT.
I quite like WoF positional, I always use it after ambush and WT from behind on a mob and it does do huge damage when it crits but it certainly doesn't go down as an essential.
You don't mention if you are going into the Moors or not, if you do want/decide to, getting the Hampering Javelin duration (minor) legacy would be useful in there but after that I would be using stat legacies.
Hope this helps, good luck
The Last Alliance - Officer
Dapple - Rank 10 Warg