First off, let me say that this is NOT a balance inquiry. Casters vs Fighter is a long, frequent, and boring topic, and not the answer I'm looking for.
My new campaign is going well, but I have some concerns about the fighter in the party. He completely outshines everyone else in combat, doing twice to three times as much damage. The rest of the party feels slightly neutered by this. While not in combat, though, he doesn't do anything, as he has no useful skills.
The PCs are 6th level, and are 20-point build. Party consists of 2-weapon Fighter, Cleric, Wizard, and Shapeshifter Ranger. The Ranger has hit a sort of dead end with his build; natural weapons don't scale well, and he lost his third one (he started as a half-orc with the Toothy trait, but a death and a Reincarnation later...). The Cleric is a new player, and so doesn't know how to trick out his spellcasting; I can't offer him advice, never having played one. The Wizard is just a Wizard.
My questions are, is this normal? Should I be throwing monsters with higher/lower AC at the party? Will the obscenely different damage potentials shrink with growing levels, or increase? I want to take the campaign to high levels; 17-18 at least being my goal. I wonder if at that level, the Fighter will be constantly frustrated, though, as combats become less frequent and campaign-straddling things are accomplished via roleplaying encounters.