There are a few abilities in the game that try and help with mana issues other than your obvious " gainer " attacks that you spam. Dark quiver is ( or could be ) one of them with the Resolve node. 4 points in the node gives you 8 mana back per arrow picked up.
The problem is not only does the skill cost 20 mana its gated behind archers focus ( which is a good thing for some builds like mine dont change ! 
) if you only took the 3 / 4 points in archers focus needed to get to resolve you are only gaining back 6 mana per arrow. If you are using the intended purpose of dark quiver of using an arrack a fter you pick up an arrow you will never be gaining mana.
TLDR i want a character to feel cohesive and not just enter generic spending ability / enter generic gaining ability. Give even more unique ways that make sense thematically for each class to gain mana back that doesnt only require a gainer. You still have the gainer / spender play style but in between having to kite around picking up dark quiver arrows as well would be feel nice.