I have not really played [Ember] since playstyle was to press 4 at the start of the mission. I recently decided to see if there was room for some weird but effective build.

Playstyle is simple:

Keep Immolation active at all times (to cap damage reduction, you will need to cast/recast it with [Growing Power] proc).
Refresh Fire Walker to stay DoT free and keep allies free of DoTs if they know how to utilize it.
Use Inferno to build up heat.
Use Fire Blast to delete armor and heal or dump heat (you don't want to keep heat at 90% for very long).

Overframe calculation for damage reduction is wrong. DR is capped at 50-90% based on heat level.

If you don't have Helminth you should really get it but... Rolling guard is preferred over Adaptation in this case.
Stretch can be used, but I prefer Augur reach for shield-gating.
Arcanes are my preference. Good exmaple, you can use grace and then swap [Healing Flame] for [Exothermic], more range or [Augur Secrets]+preferred aura.

Build worked great at highest kuva liches, did not tested it in steel path.
Enjoy