In my opinion, a speed of 5 is quite slow... Although it won't hinder early development, as a rule, few players have water creatures in the first or second week...

So, I've been reading reports on online games in HoMM 3 and some tournament games in HoMM 5, and I've come to the conclusion that in HoMM 3, the bonuses and penalties for movement due to creatures are much more significant, so players carefully monitor the composition of their army. But in HoMM 5, in the early stages, almost all low-level creatures have a speed of 4, and less often 5, so none of the elemental types, if present, will be a hindrance. Moreover, their combat power, even if they are the slowest in the unit, is always a higher priority than a small bonus to movement. In online games on the standard map, the presence of elementals in the army in the first weeks almost always occurs - it's a good addition to the strength of a small army. That's why, from a practical point of view, I also prefer elementals among the neutral creatures (just to stay on topic :)).