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Don't forget that there's one more Twilight/Astral Dragon! This compensates for their weakness, and in general, even though they are weak, they are still a level 7 creature, so I think you are wrong to refuse them. As for 1-2k skeletons, this isn't Might and Magic III; here, that's not enough, even a skeleton specialist isn't available (which is a pity, because Galtran was my favorite hero in Might and Magic III).
It's not just one hero, but 1-2k is a small number, but if you have magic to create clones and enough mana, these 1-2k can turn into 2-4k, and I think it will be difficult to defeat them...
Added 4 minutes later
6. Death Bringers (Banshees, in my opinion, are not worth it; their scream has a range of 3 cells and takes away very little HP. IMHO, Death Bringers are the best)
But Banshees attack everyone within a range of 3 cells, and keep in mind that no matter how many Death Bringers there are, their special ability will only affect one target, and many Banshees can handle this...