How to effectively use quick battles (autobattles)?

the hero has Expert Water and Earth magic and the spell Forgetfulness, has the Medal of Vulnerability, the army is not great but there is a fast flier, so I have the first turn, I break the neutrals — Liches, since I have the first turn, first comes Forgetfulness, then Mass Slow, and then winning without losses is just a matter of time, but with quick combat the result is completely different...

for example, when 100 Pixies wipe out 900 Magma Elementals with Alchemy and the hero having the necessary spells and skills, if you set quick combat, the result will be a defeat....