The banshee already has 200 health and high defense – the messengers are only slightly stronger in attack, but considering that their defense and health are lower, no one will take them. They are much weaker.
I think the Messenger is a finished concept, the banshee needs adjustments to its defense and health, and its wail should be reduced a bit – let it be 180, like the Messenger's health, and reduce the defense by at least 5-10. And the wail deals an unreasonably high amount of damage (and there are THREE of them).
But the banshee is different from the Messenger in that it is more durable (+ health and defense), but at the same time, it loses attack and damage. I don't see the point in making the two alternate upgrades equal – the Messenger feels great in the thick of battle, dealing huge damage with quick attacks and frightening nearby enemies, while the Banshee is strong in defense, and when an enemy gets close, they will receive a spell in the face.