A shieldbearer and bishop allow you to take whatever else in the 4 slots for basically every single fight in the game with the exception of the double Jean boss, which I'll add my 2 cents to the pile that it's the only boss fight I actively hated. It has way too many immunities in its first phase for a boss that also ignores the frontline/backline mechanic due to using almost exclusively aoe magic nukes. Were it not for the fact that stuns aren't part of the immunities list, it would legitimately require dying to it first to learn its mech to then build a team specifically for it.
Personally, the best bosses are the ones that play by the game's core mechanics of having a full team. Dwarven coalition fight was my favorite since they essentially were a player party you had to dismantle.