It was on insane.
I just started a new game earlier today to give it a second try. This time remembering to save often 
Custom Tinkerer with Varda as hero, Chant of Vitality, 7 chaos, 1 enchant.
Tinkerer because of Master Archivist and more enchanting slots. I beeline for this since it gives me sovereign skills and lore by questing and hitting treasure chests. Super useful with Chant of Vitality.
Varda because she has the best mobility of any hero in the game.
7 chaos for +5 mana, +10 dodge, +15 accuracy, +3 hp. Lots of good enchants in chaos, but has very sucky spells overall, which is fine as the enchantments when all combined together are seriously op.
1 enchant because of city and unit enchants. There's also a city enchant that gives +1 logistics to a city. It doesn't cost any essence and is stackable. Basically gives you infinite logistics. Unfortunately, my current game didn't have the luck of having that spell, so I'm going to have to city spam and hope for the best. 
Start of the game, I rush to find enough mats to craft something and start enchanting. I got lucky and got a short sword from an early quest which boosted Varda quite a bit. Got some defense rings. Prioritized getting to 100+ dodge, then 15 mana per kill, then 9hp per kill, then as much accuracy as I can get.
Switch all shards to boost sovereign skills. You'll soon be learning spells faster through questing than shard points and mana from shards is tiny compared to what you get from mana per kill.
Got double-lucky by starting right beside the SK's fortress, so I could take out his troops very early, preventing him from expanding and destroying shards. This will save you shards in the early game more than anything else. Even if I didn't start near the SK's fortress, I would explore on a single turn using chant of vitality until I find the SK's armies and start taking them out. Easier to find them when
I'm at turn 18 and Varda's already at level 11 because of all the SK troops she's been killing
. Watch out for warlocks though...those guys hurt. They can seriously kill you if you don't kill them on your first turn. Other than them, everything else so far has been a cake-walk, if a bit tedious due to all the fights.
Once my mana income started flowing, I just spent mana to build instead of production. Gets logistics up fast allowing for the pioneers to come.
I'm expecting any 100% strategy on insane to get nerfed, so enjoy it while it lasts!