Final slot Is [Biting Frost], overframe just doesn't have the mod yet.

Why Thermal sunder subsume?
Thermal sunder freezes enemies which counts towards biting frosts augment making it incredible ease of use in content where nullifiers don't rear there ugly heads.

General Gameplay Loop.

Use sunder to freeze then shoot enemies, and if you're on steel path, endurance runs, anything that becomes a little tanky, use avalanche to strip 90% armor on all enemies.
Snow Globe to protect objectives or yourself while casting/being damaged.

Overall just experiment and do whatever you want this is just an idea I had.