Round table

Basically, you can compare by HP and damage:
2 hydras
vs
9 bulls + 2 vivs + 2 vasyks + 8 flies + 12 lizards + 16 gnolls (if I remember the SoD numbers correctly).

It's not just about HP and damage here, but also about the price. It's easier to buy up two hydras, and you can already get things done with them. But the fodder still needs to be bought out. In SoD, the economy is worse after all, since scrolls aren't replaced by piles of gold and there is no bank. (there will be +4 crocodiles, and +9 lizards, I think)