[Is there any lore behind WvW aka the Battle of the Mists?]

There's also that weird thing where in a renown heart event in the Domain of Vabbi you tell a student how Mordremoth died by having its head impaled, i.e. telling the story of the open world meta event rather than the instanced version. Up until that point I had assumed that the meta event is not canon.

That's cool, I must have missed that. I think I know the event you're referring to though. My head canon is that each map is a fixed point in time, repeated over and over. It kind of clicked for me with the jahai bluffs event where the charr and humans are locked in a repeated battle. This also fits with the idea of a multi-verse I think.

[Is there any lore behind WvW aka the Battle of the Mists?]

Three (or more) alternate Tyrias are fighting each other in the Mists. These Tyrias are not exact copies, however, major events and important roles always occur.

So technically, each server could be considered a different reality in a multi-verse.

[My thoughts on the personal story, namely Trahearne and the Commander. (Spoilers)]

I'd recommend checking out wooden potatoes on yt as well, he has a ton of lore videos, including S1 of living world and play throughs of most releases.