I got to round 28 with only no pro bonus (somehow legit), and I do have one complaint. After round like 20 when you get the sixth party member, the game feels like it is just a sit still and wait till you die since I don't think you unlock new character slots again, would it be possible to add more party members to use in later rounds?
Maybe like you can spend money to gild a party member to do slightly better or just more party slots.