If you were going to give an archon a blast pistol, I suppose it wouldn't be a bad idea to also have the parasite's kiss. They have different ideal targets, but they can both shoot at infantry.
That said, there isn't a situation where I could imagine I'd recommend taking a blast pistol. It's got a 6 inch range, 2 inches less than a haywire grenade for triple the points cost. And if you REALLY want a darklight weapon, an actual blaster is the same price for triple the range.