I think ultimately it came down to the QB, but their talent eroded pretty rapidly over the years. They took a lot of big, Madden-like swings on players rather than smart, meat and potato type additions.
McDaniels strikes me as one of the few new-wave young coaches who is still committed to the running game. He just does an awesome job working people open and mixing up his formations/attack.
Give him Herbert, a good (healthy?) offensive line, Hampton, and that WR room? Yeah...I think the Chargers could be dangerous.