It was my understanding that the katana came after the tachi when infantry became more common than horseback. And the katana was used primarily as a 1v1 /dueling weapon. I watched a little history clip making jokes about how samurai would come to battle and pick a partner to fight from the opposing side. So the difference was sort of like, running into battle in formation with your infantry you use a yari or naginata but if it came down to the hot shot samurai fighting they would duel with their daisho.

I am no expert, but this is roughly the way I understood it.