Just did another playthrough, I managed to get to the last boss using Tuskal (tier 2), Tizik (tier 2), Gheist (tier 3) and Karakei (tier 2), and then I lost.
I learned 2 things:
- Technicals and Defensives are very strong, Aggresives are there to fill out your team.
- It's best to use a maximum of 4 Monsters, and try to get them all to tier 2+, with more importance on maxing out the Technicals.