Lone Wolf + Glass Cannon is actually less powerful than four people in your party by middle/late game. Ultimately it is a very fun alternative way to play the game.
But if you want to increase the difficulty? Go with Two Characters with No Lone Wolf or Glass Cannon.
For me, half the fun in a RPG is building the character however I want, to have to worry about being too powerful in the hardest game mode, is usually a design issue.
