I've never had a PC expert, but I did GM a game where one of the PCs was a single-classed Akashic (Arcana Evolved) with none of the combat-related abilities. He had a *very* non-combat focused LA +3 race (the undead eleti Mythic Races).
He had, IIRC, one kill in probably 25-35 sessions. All but I think maybe 1-2 of those sessions involved at least one significant combat. He was OK defensively only because he was uncrittable, meaning he didn't go down in one hit and had time to run away, but he had essentially no combat skills whatsoever, nor a single combat-related party buff.
Yet that character was the second- or at worst third-most effective and important PC in the game, behind only the party leader/combat monster paladin/shadowbane inquisitor and probably tied with the rogue/assassin.
The PCs were in an enemy city and the enemy knew where to look for them. This character hid the party so effectively that an epic-level counterintelligence agent COULD NOT FIND THEM WHEN TAKING 20. Even knowing they were in the building (a captured PC gave up the info to an enemy psion), he simply couldn't beat the Hide check and had to give up the search.
This character also had a habit of disguising himself as the party leader and the party leader as another character - his main contribution to combat, because enemy snipers with the IK Rifleman class would routinely be frustrated at the party leader's apparent immunity to their auto-critical ability

. Sometimes, he disguised every member of the party as a different party member. Other times (such as when the party leader was briefly serving as the regent of the PCs' country, the leader of their armies *and* their emissary to his church), he disguised multiple characters as the party leader to throw off enemies (he acted as the regent in this case).
This character routinely forged documents that completely altered the political landscape. He incited a rebellion against a hostile regime that had taken over the PCs' country (leading to the aforementioned regency), instigated a war between two hostile countries, got the PCs entrance to multiple factions, etc.
With this character in the party, the PCs were literally never at risk of discovery until they began an operation. His disguises were literally perfect, his bluffs just as good.
This character's knowledge skills were also almost all maxxed. Certainly by the end of the campaign there were no published Knowledge DCs he couldn't meet with a roll of 1.
So yes, a purely skill-based character who has no fighting skills CAN be a perfectly valid PC, even in a combat-heavy game.
