I want to apologize if there is already a threat on this topic. I don't really know how to check on that.
So I've just watched the WoR Vale and it just keeps me kinda wondering where Grimm actually come from.If the mountains can protect Vale against them, then that means they don't just spawn outside your village if nobody's looking. They have specific places somewhere beyond the mountains where they originate from.
If I think back to volume 3, that Grimm dragon was able to give birth to other smaller Grimm. What if there are special places on Remnant that are actually the homes of "big" Grimm like this dragon. The four schools were built on four of these places after the Grimm living there were defeated which then caused the area to be rather docile and enabling people to settle there --> the 4 kingdoms. This then means that
a) There are other big Grimm like that dragon who are currently not frozen etc. but active; otherwise there would be no Grimm.
b) If Ruby hadn't frozen the dragon and the tower had fallen, Grimm would have spawned inside of Vale and the kingdom would have been lost.
Maybe that's why Ozpin wanted to protect the tower at any cost.