I would actually recommend against the lone blaster. That's a lot of points for a single special weapon, and while I don't believe in "points investment versus points return" I think there's more they can do. The archon's big sell is that 2+ invulnerable save that on a good day can really swing a game sometimes. Give him the shadow field and and an agonizer and go to town supporting combats as needed, or just tying up nuisances for a round or two, like devastater squads/havocs, that sort of thing. I wouldn't sweat ap3, the new design convention is to make a 2+ armor save more valuable, and quite frankly if you weren't just lancing those targets to death in the first place you were being a little reckless haha.