For example, in WGE, Nargott used reduced movement speeds to balance the movement and make it more interesting, but as I understand it, he reduced the speeds because he couldn't increase the size of the arena. In 5.5, the arenas have been enlarged (using the sizes of siege arenas), but only in battles for structures.
I would also like to note that with enlarged arenas, the number of cells on the field increases, and thus the tactical role of each individual cell is reduced, including the role of unit sizes. The only reason I would like to try larger arenas is the possibility of placing more large units, i.e., from 10x12 to 12x12 or 14x12.
But if we were to fantasize, it would be cool to see hexagonal arenas with a reduced number of cells, similar to Heroes 2.