Which Might and Magic universe are you referring to?

I disagree. I actually liked the sphinxes (even though they were incorrectly named lamassu; they are essentially dead sphinxes) more than the spider-legged creatures. Before the game was released, I even hoped they would be new champions, but it wasn't meant to be. As for the sixth-level unit: we have to admit that both the Death Knights and the Undead are quite good units, so it makes sense to keep at least one of them, or even both.