Andy is one of those characters they never wrote consistently. The Andy you see in one season bears nothing in common to the Andy you see in another. Kind of like Ryan. Ryan started out as this guy who knew all the business theory but had no sales ability. Then he turned into white needy Tom Haveford.
But it's sure not Ed Helms' fault. I really think they kept him on because he was played by Ed Helms.
Anyway Dwight was always the real main character of the show, especially after Michael left.
I wish Pete & Clark joined sooner. They should have had time to be fully developed instead of being The Office's Ezri.