Play as Inferno.

The first tactic is certainly not bad, but here, luck plays a role (whether raising the dead will work, whether defense will trigger, whether evasion and bonus damage will be granted).
If everything aligns, it will be great (considering the situation without war machines).
However, gating units and having one strong unit is debatable; by the time they appear, the enemy will have already managed to inflict significant damage on your troops.
Ask yourself, do you actually use this tactic often in practice? ;)
You need to seize Utopia, as mentioned above – gold/artifacts/spells/experience – this is where Darkness really helps. You need to pay attention to troop placement (some dragons can reach their target in one turn). By the way, Keen Intellect is a truly excellent skill here. =)
There will still be losses, the question is how significant they will be. For now, I don't see a universal solution. It's better not to venture in without Darkness; protect small creatures (like imps/dogs). If dragons target imps, it's guaranteed to be frustrating.

Well, basically, it's hard to come up with anything truly good; everything depends on that "if."

The second tactic, with losses, is interesting. =D It's somewhat masochistic, but in theory, it sounds quite good; I'll try it today.
Although, I hate losses. I even cling to a single Imp; I don't know how it will be with dogs – will it cause an immediate heart attack or later.
And what is your priority at the beginning of the game (luck/defense/attack, or Darkness in general?) I try to take luck first, because lucky attacks from Gaters often help a lot. And in general, I think that luck suits demons even more than it suits dwarves (Wide Gate of Hell is a wonderful thing), and dwarves can even manage without a soldier