Might & Magic: Heroes 8 - to wait or not to wait?

No, levels are needed, even if not formally. This is a way to differentiate creatures by strength, and it should be clear and obvious. In the fourth game, there were 4 levels, and that turned out to be insufficient; some units, like elementals or zombies, occupied an intermediate position, but within the castle, there was a clear division based on stats: the second level was noticeably stronger than the first, and so on. Now, it's a bit strange that, for example, a fairy is comparable in strength to an archer. Traditionally, fairies are almost the same as peasants, only with ranged attacks. Even if they balance it within a level through stat increases or abilities, there should be very significant differences in parameters.