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Regarding the wolves, I think everything is fine here. They may be highly proactive, but they aren't very fast – they can't reach you in one turn. Therefore, you need to attack them first; they don't call for reinforcements during a counterattack. As for their initiative and the ability to attack in a pack, that's also understandable. Wolves are quite proactive in nature. And when they howl, a whole pack will definitely come running. Perhaps, the summoning of reinforcements could have been delayed, not happening immediately, but after half a turn (like the demons' gates).
As for the Earth Elementals, the developers didn't really mess up. Yes, their initiative is low, but they have quite high speed, powerful attacks, and endless retaliation. So, if you don't take them down with ranged units and attack them with melee units, it can be very painful. But I consider the Water Elementals, with their ice arrow, to be cheaters. They've annoyed me since Heroes 4. They have quite high initiative, and it's so frustrating when your army is 100 times stronger, but you can't get past these water elementals without losses.
As for the Phoenixes, I agree – their abilities are definitely exaggerated. If there are only a few of them (say, up to 20), you can still fight them. As a Necromancer, you can even try to get through them without losses by using Blind and summoning the dead. But I was once playing the scenario "A Dance For Two" (maybe someone knows it, it's quite interesting), and there I ran into a small detachment (about >500) of Phoenixes with a decent army (about 15k skeleton archers, 250 liches, 150 undead, about 1k ghosts, and almost 100 skeleton dragons) and was brutally defeated, even though I had recently defeated a similar number of Twilight Dragons with a slightly smaller army without any losses. After that, I abandoned that scenario (it's a pity, I was enjoying it before) and said that the Phoenixes need to be nerfed, and nerfed again.