Do creatures you buy through the Altar of Wishes get assigned to your main Hero on each map? I am wondering it they are really worth purchasing. If they are faction specific this could lead to a large investment if one is planning on playing every faction. If they require pre-built structures, then it would detract from the advantage of purchasing them through limited dynasty tokens. In my opinion, the start game is the most crucial factor in a decisive victory.
You cannot buy creatures in the Altar of Wishes. What you are purchasing is a creature's icon which you can use in place of a hero to display in your Dynasty.
Like titles, they're essentially worthless, and since you can't buy everything in the Altar of Wishes, focus on the Dynasty Weapons and Traits first.