These two weapons can be extremely potent if used correctly, but they're simply annoying in parties. They basically create giant blue explosions that obscure vision and make it extremely difficult for teammates to target an enemy. I want a visual nerf; keep the mechanics the same but tone down the dramatic explosions a little.
The Leviathan might be an annoying weapon as well, but at least the charge attack (the annoying aspect of this sword) doesn't visually hinder teammates.
Just tell the teammates not to spam Polaris and Nitronome.