[Radek]

Custom characters are always stronger than the predefined ones. Reason is clear. They are well created so that they have better stats and, from the point of the player's wiev, their proficiences and skills are distributed better.
If you have found a party of 6 custom characters rather boring then reduce the number of characters in your party. I like to play a party of 3 dual class custom characters:
ranger/cleric
kensai/mage
swashbuckler/fighter