The widow has a lot of HP and does pretty good damage but the incarnate has better abilities, can CC (and in this game CC is king) and you can give him back physical/magic armor by buffing him during the fight, making him more resilient to CC (and again, in this game, CC is king).
In the end, I only use the widow when my incarnate is on cooldown or if there's no blood around (since the blood incarnate is my favorite).
