I beat Molly on hard. It was pretty brutal.
I also bought everything, and got every class to 40. The temple door says it's not finished for me either.
Gabe is the best physical damage dealer in the game with Masochist Str up -> Tube Str up -> Power Up -> Pulverize, doing about 55k to 75k each time he does it to enemies that have been Ichor'ed by JIm.
You can also land tons of damage by using Terrastigma on a single enemy like 3-4 times then using Entomb over and over again while equipped with Living Salts/Earth/Whatever.
Moira seems like the best as cordwainer/elementalist.