December incoming PLD changes are not useful

[SubDragon]

Does this mean banish spells will finally get an update to be something other than trash? Because at present, they are horrible for the MP cost and a waste of 3+ seconds not doing anything else.

Banish was never about doing damage.
Banish reduces the special resistances for physical attack types on Undead so your physical damage of types like slashing do more and lasts for increasing time the higher up the level of Banish you cast.
It was never "Trash" but it sounds like you simply lacked the understanding of how the spell was designed to be used and special resistance system on mob families and not on the magic itself.