Box formation is the least useful formation out of the 4 AOE2 formations. Nobody, not even new players who just picked up the game, uses box formation to “protect weaker units on the inside”. It is, however, to keep a small number of units together when microing, but as soon as unit numbers grow to a point where a clear empty space is formed on the inside of the formation, players ditch box formation and go back to line formation instead (nobody likes the empty space).
It would be much more useful for box formation to form a solid box instead of empty box (see picture).
I wouldn’t even mind using that as the default formation.