Fortunately, the Sun Soul Monk solves the most obvious problem: enemy is standing in bright light (no shadows) on the other side of A Bottomless Pit, bow-and-arrow'ing you. SS can shoot back (to 30 feet anyways).I think a party of Monks would struggle in a lot of situations.
5 Rangers, particularly 5 beastmaster rangers, is definitely the correct answer. What would make for more of a puzzle though is what’s the worst party you can make of five different classes (again, assuming they’re all competently built and played. My instinct would be Barbarian, fighter, monk, rogue, and maybe ranger or warlock, just to give them the least access to spells possible given the constraints, but I don’t know.
Yeah, but no version of the rogue can heal (outside of the Healer feat), and the spellcasting version doesn't have a lot of utility (limited spell slots and spell selection). You would be all stealth and sneak attack - which is great up until the point something goes wrong. The main weakness is relatively low AC on most rogue variants and limited ability to heal in combat.