Which level 7 creature is the best, and why?

but in practice, it turns out to be the opposite... especially in tournaments)

In practice, you can defeat anyone, even with Bone Dragons! It all depends on different game situations – sometimes one strategy is more effective, and sometimes another. Don't you agree? Even if you look at the regular ranking in Heroes III, Archangels are in the top spot, and that's hard to argue with. Although the ranking itself has some uncertainty...