This makes you understand how the whole event was badly conceived.
Let's talk about some improvements:
Guild tech should be reset at the end of the DE to allow all guilds to start at the same level next time.
Create conditions that block massive Act Again and other various types of "cheating".
Penalties, even serious ones, if you do not conquer all the external and internal zones before attacking Baldea, or a system that forces you to leave a certain number of units on guard in the nodes already occupied if all the other accessible nodes have not been conquered in that moment.
Remove faction bonuses. An interesting thing about DE is being able to use any unit without worrying about faction buffs, but the faction bonus partially penalizes this feature.
Speaking instead of more absurd improvements:
Allow the participation of all guilds, even the weakest ones that have not completed catastrophe.
Introduce a difficulty system that varies based on the guild's average strength. The rewards in the store will, of course, also change based on the strength of the guild. A low-level guild for example will not have access to SP materials, etc.
Replacing the stupid supply system with something that doesn't lead to game over if you make mistakes in unit management.