Stasis is most definitely an Element type, as much as it is an applied effect type. Also dunno why you mentioned "the other two", since three of the Light subclasses do synergise with Osmosis. Contact with Stasis in any form is inherently damaging, it doesn't just form shards of normal ice. Stasis fields produced by Duskfields are corrosive, Stasis kamas of Revenants are heavily damaging (esp Silence) , the shards of Glacier grenades deal damage in multiple ways, Stasis Bleakwatcher turrets also deal damage in addition to applying the freezing effect, etcetera. Long story short, it's obvious that practically speaking - Osmosis can most definitely synergize with Stasis. Bullets enveloped in Stasis would carry corrosive elemental damage. Far as the topic of Balancing goes, that's up to how well Bungie balances it out. It's not entirely out of the question to have Stasis weaponry without them being OP.