I'd love it if there were bosses in the dungeon that could be skipped altogether.....
And the 5th chest was obtained from killing all bosses

For instance, In Cutter's Cry... You have to kill the Myrmidon Princess and the Chimera within an hour....
What if the Myrmidon King/Queen was an optional boss... one that you could skip altogether... but killing it got you that 5th chest