Use Thurible at start of mission/wave, [Harrow]'s passive gives you 100% of your energy at start of mission, then spam Thermal Sunder. Fire procs from it will strip armor so no need for big numbers on strength. Bring weapon that will give you first kill after casting or interrupt casting to preserve some energy to cast Thermal Sunder. Remember to recast Thurible BEFORE you run out of time on it and in consequence energy.
And remember DPS or not you are still Harrow - use Penance and covenant to help allies!

Also remember that we are going to deal HEAT damage not COLD damage using sunder: remember to invert casting in options for GAUSS - Thermal is Gauss ability, not Harrow's ability.

Go ESC -> Options -> Controls -> Invert Tap/Hold Abilities -> change Gauss from DEFAULT to INVERTED -> Save config -> Done, you are ready

Options:

• Use lower rank overextend (I use rank 3 for 104% strength for other abilities)
• Use any aura you like, for this build [Corrosive Projection] because of polarity, and I wanted to keep this 0 forma build (I use Brief Respite to recharge shield after I use Penance, but it require aura forma or forma).
• Feel free to include mods such as streamline for increased ability efficiency.
• Thermal Sunder is on slot 1 for ESO - Simaris WON'T get mad if you spam ability 1, if you use slot 2 (or other) for Thermal Sunder he will block it for a time, so keep it there and gain overshields using Augur set bonus instead of Condemn. (For other modes such as regular SO or defense feel free to swap other ability)
• Use Augur Pact and Augur Seeker on your pistol to get 160% energy to shield conversion (and overshielding).
• You can swap overextend for Augur Accord for 200% conversion, but your range will suffer from it.
• You can slap exilus mod such as Cunning Drift, but you will need Adapter and possibly forma to fit additional drain.
• Growing Power as aura is also nice option, if you wish to go for it equip high status chance weapon to activate it.
• Molt Arcanes are great to increase increase efficiency.
  Side Note - Beware of Nulifiers!

Clip:
I will upload clip form ESO later on.