So, this was probably my hardest mission so far. Difficulty ~47 iirc, I was 15T under tonnage and I killed about 100K additional enemies, before leaving. Far from my best performance, I got badly mauled by a Charger + Trebuchet combo, while my lance was more or less deployed on the other side of the objective.
As you can see, even if I clearly did the majority of damage, they are pretty good if you give them specific target (aka killstealing). Don't mind the Dragon, it's... highly experimental... also, it's there to somewhat inflate tonnage and soak damage (which it miserably failed at doing).
This mission was an outlier though, I killed 10 or so 'mechs, hence all dat damage (and salvage, a pity for the heavies)
And here's my firestarter setup, In case you're interested:
Here's an example of a Warhammer I just got from a story mission and how I would set it up.
I lack a Warhammer to experiment with atm, generally speaking though, choose a favourite engagement range (L, M, R ) and go all in. I find that med range favours armor, SRM and AC, long Range favours missiles (if you use sensors correctly) and PPC/LL, close range favors energy weapons and speed.