Just like in Well of Radiance. Bubble is made near totally worthless when you can easily get frozen and melee killed instantly. Just make it so that when you have the "Armor of Light" buff (only available when inside of a bubble), you can't be slowed or frozen. You already can't shoot out of it, so at least make it somewhat more of a defensive super.
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Personally the only thing I feel like should make you immune to stasis is exotics, I don't mind well as much now since you can break the sword even with the supers. Bubble does not need immunity since it forces the user to go inside, after that its a who plays their hand correctly moment. As a side note stasis already recharges slower than all light abilities.