Without a specific map type and victory conditions between two players, the question of racial strength is irrelevant, in my opinion. For example, let's compare Humans and Necropolis. 1) If we create a large map without gold mines, then Necropolis is stronger. 2) If each player has 2-3 gold mines, then Humans are definitely stronger, due to training, while the Necropolis will soon have nowhere to spend their money. 3) The presence of random castles in the area makes Necropolis stronger than all others, because due to "conversion," any castle is almost like their own, while for all other races, a foreign castle provides no more than two gold mines. Conclusion: The race that the map is tailored for is the stronger one.