[Zigûr]

I've always had the impression that Orcs varied quite significantly in size, but that in general terms they were shorter than Men. Otherwise the height of Saruman's Uruk-hai would not have been noteworthy. To the same degree, Frodo and Sam were apparently able to convincingly disguise themselves as Orcs in Mordor, which suggests that Orcs could also be rather small. Even the larger soldier-Orcs of Mordor, Sauron's Uruks (which seem to have been different to Saruman's), appear to have been short and broad with long arms, as Grishnákh is described as being.

On the matter of axes, it might be worth noting that Dwarves and the Men of Lossarnach were not the only ones to use them. In the First Age the Elves of Doriath are described as having stores of axes alongside spears and swords, albeit after they met and began working alongside the Dwarves. Beleg brought "great strength of the Sindar armed with axes into Brethil" to the aid of the Haladin.

However, the Noldor smithed axes as weapons in Valinor before they ever met the Dwarves.

Incidentally, it might be possible that the Dwarves would deploy weapons like spears if they encountered Men or taller opponents, and favoured axes in their more common battles, which seem to have been against foes of more manageable size: Orcs and each other.

Nonetheless, I tend to think that the representation of Dwarves as using axes is more a literary device intended to make them seem exotic than a matter of realistic tactics. That is not to say that Professor Tolkien was uninterested in that kind of realism, as I believe he was, but in this case I feel like the concept is perhaps more poetic than necessarily realistic.

Personally I tend to find the idea of the Dwarves of Middle-earth fighting with swords and spears and mattocks alongside the axes more and more appealing as the years go by because knock-offs of Middle-earth have turned the association of Dwarves with axes in Professor Tolkien's work into a tiresome, obsessive cliché. As for Dwarves being depicted fighting with war hammers of all things...