This stage held me up for a while. I thought I might have to grind a MASSIVE amount to beat it but it turned out I just needed a better strategy. I learned about the throwing technique shown in a video and decided for my team, having the mage destroy the two geo pyramids would be the best chance I had. After failing with other characters. The mage can destroy both pyramids with one magic spell. Taking more than one turn was lethal for my other characters as they would get annihilated by the time I destroyed all the domes, if I could even do it before being wiped out.
I didnt time this mission but it took alot of tries and I tried it on several occasions. Around 2 hours just today.