Applying Wither as bow user

Hey folks,
I would like to ask your opinion on what is best method to apply Wither debuff as bow user?

I'm currently using Vaal Rain of Arrows (ROA) with Divergent Withering Touch Support. I have also used Blast Rain as an alternative to ROA. I can not determine, which one is better at applying the debuff but RoA definitely feels better to use due to its faster hit and bigger area coverage.

I'm interested in bossing now so I'm looking for option that is best suited to apply and keep high amount of Wither stacks on single target.

Would it be better to swap to spell totem with Wither instead of bow skill?

I personally use Spell Totem + Multiple Totem + Wither + Faster Casting myself on my Toxic Rain character. Works very well imo.