I beat Brigandine (PS1 SRPG) on hard, with Leonia, doing a no recruitment run, and doing no attacks until I recruited Aldis, meaning most of your starting monsters get whittled away by upkeep while you sit around with only one castle. It was fun, although unfortunately it still has the same problem as the main game, that once you can get rolling the difficulty falls way off. At least the time limit is an issue for a change.
I once saw a guy that claimed to beat it with knights only (no summons whatsoever) but after playing it as much as I have I find that hard to believe. I do want to try a "all knights must attack every turn" run at some point though.