So with the release of edge of the earth there is new life injected into old cards as ever and I am here to try in vein to prove every card has its place, now the place wither occupies is a niche one, but less niche with a spicy little hotness.
Wither is worse than Swordcane because you can't evade.
Wither is worse than Katherine(+big spell) for lack of damage.
Wither is worse than Knife because even knife is cheaper.
Well.... Wither is a Spell and that means it has nice place besides (one of my new favorite cards) Prophetic, it now can be played for free and can give a boost to attack, if you are running Prophetic anyway (you should, its amazingly powerful) then wither I think just out competes a lot of other side weapons you'd use to finish of enemies.
A 0 cost asset that is very easy to search out of your deck with other good mystic cards seems like it could easily pay for itself, in Dexter you likely won't even end up losing an action to play it, and if you are going Dragon Pole route it gives you a very cheap approach to filling your slot with an emergency method to attack.
ALL this said.... Brand of Cthugha is an absolute monster of a card, which also only costs 2...so maybe wither will never enter the spotlight and just warm the bench for the new brand, but it has a use that's worth exploring and considering.
Edit: Two card corrections. C>K, Sword Cane>Dragon Pole.