Yes, indeed, you can use griffins to counterattack. It's especially interesting to throw them right in front of the enemy, and the more they attack, the worse it will be for the enemy, although I doubt anyone other than the AI would fall for that.

As for paladins and archons... I think the new mounts are better – very often you have to attack from two squares away, plus they deal more damage... you send them straight into battle, and the archons heal, that's all.

Really, often? I practically never use this ability, even with defender archers, it doesn't always work. And I think the damage is the same. But this ability is still better than the one the old ones had.

I'm saying it again, IMHO, the seraphim is not meant to support paladins. Sometimes it can hit harder than paladins, and besides, Divine Retribution is a powerful spell, even if it requires sacrifices from your own army.

Exactly, sometimes. And sometimes it's worse. Besides, I rarely use the magic of spellcasting creatures, except for a few; it's better for the hero to cast spells. Warriors usually have plenty of other work to do.

If seraphim had retained vampirism, it would have been overpowered.

I was talking purely from a stylistic point of view. Angels are meant to resurrect. And vampirism could have been weakened.