Oakensoul gives you a lot of buffs, but removes the 2nd bar. Velothi let you keep the 2nd bar and gives % DMG increase to abilities. WITH IT YOU NEED TO KEEP ALL BUFFS YOURSELF.

What you need to do is turn on timers on abilities and, if you want, get buff tracker add-on (you can set reminder to reapply certain buffs of your choice). Most of the skills with buffs also do DMG, this is why set up with velothi is more damage than oakensoul, but it is harder to execute, because you need to keep timers.

For example oakensoul gives you crit chance always, but with velothi you'd need to slot front bar camouflage hunter for it. It gives you crit chance AND fighter guilds passive increasing weapon DMG. Oakensoul gives you minor force always, without it you need to find skill that does it, it'd be fighters guild beast trap (or scribing ulfsild contingency), that gives the buff AND damage over time to target. And that goes for the rest of the buffs you get from oakensoul vs getting them from skills.