Terrains could have more of a role in the missions too, ala Shining Force, and Possibly with the Geo Symbols that Disgaea had going on at the time. Basically, there could have been more units, but the elements, which play a major role in the main game, should have been used in the Liberation Mission maps too.
A cracked panel on the overworld or two would make the player think otherwise with his melee fighters.. but most of them were RANGED. It would've been nice to have Junk Man units or Norm. Navi units as extra help, considering how annoying it was to clear a dark panel in three turns if enemies had the vantage point (more dark panels surrounding you, etc).
Yeah, what's the point if terrains only affected the battle screen and not the main overworld, aside from the "Dark Panels", which could have been perfect "Douche Panels", which harm you and heal your foes on the overworld like a normal poison field would.