How to make Banshees viable with minimal changes:
take the current passive, and replace it with the Unique Nights Veil passive, which is the unique passive on
Now you can create your spell shield when you are looking for a decisive fight instead of having it popped by one ez Q, it has a 40 second CD, which current banshees has, but it comes back in 40 seconds after activation regardless of what happens, while taking damage during banshees down time resets the counter
So for those who dont know, here is
current passive
UNIQUE: Grants a Spell Shield spell shield that blocks the next enemy ability. This shield refreshes after no damage is taken from enemy champions for 40 seconds
and here is
unique passive that Banshees should have
UNIQUE – NIGHT'S VEIL: Channels for 1 second to gain a Spell Shield spell shield that blocks the next enemy ability within the next 7 seconds (40 second cooldown). Damage will interrupt the channel. You can move while channeling. If the channel is interrupted, the item is put on a reduced 5 second cooldown.