The most difficult alternative

Venoms are also useful when you need to quickly upgrade a Castle to level 4! In that case, they are preferable to Vampires. If I'm not mistaken, in Equilibris, Venoms became much faster, not by a lot, but still. And you don't necessarily have to move them around; it's enough to move them yourself to the location of the expected events and only then join them to the main army, thus saving moves, days, and time. And the fact that Vampires were "nerfed" in Equilibris is already well known. Therefore, in my opinion, Venoms are preferable in most cases.