Because griffins are weak and always retaliate? Against orcs, which retaliate against retaliation and are physically strong, that means a lot of hurt.
About Bolo's bears - had problems with them too, initially, but my mage was underdeveloped then. After getting some spells... It was hard not to kill these bear too fast. Besides, something good (demanding) as an enemy doesn't mean it will be good as your troop, the same goes with opposite situation, weak enemies can be deadly when you command them. Maybe you have a knack for chickens
My recent case is army in tower of Dark Mistikus. There are two - one is lethal and one is only very strong. With lethal one I win without losses easily. With very strong... I tried many combination of my actual troops and nothing really worked. Why? They have 4k of skelly archers and twenty sometime bone dragons. Skelly archers kill 5 green dragons in one shot (or five runemages), dragons poison all troops with heavy posioning, and kill many. My best was to lose only 5 demonologists. My worst - I lost whole army (paladins, demonologists, e.beholders, royal snakes and runemages, I carry 6 runemages, and two ancient phoenixes with ). I had no problems with guys like Hagni or Spider Boss with that army, or invincible other armies. But does that mean that skelly archers or bone dragons are good? Though I admit that bone dragons are better now.
Ancient vampires are trying to be my menace too. One stack of these guys killed my phoenix, which had like 1500 HP, and vampires were damaging 200-300 HP per attack. All that by retaliation - I attacked vampires with phoenix, it missed, vampires retaliated, and again, and again. Vampires have cheat death, which makes them avoid critical attack. It was very disparaging, because I wanted to kill them with mages, beholders, other shooters, and most of them was missing always, because they had high critical.