So Nasus conveniently left out HOW Shurima fell in the first place...

I thought it was because Azir's disrupted Ascension Ritual went awry and caused a magical explosion or something? Wasn't it on the facebook slideshow thing?

As said above, they put these images on their facebook page and perhaps elsewhere too: https://www.facebook.com/leagueoflegends/posts/10154704931060556

Care that the story is likely supposed to be told from the POV of Azir. That's the argument I read they used to justify the fact Xerath now looks like your everyday boring villain without the moral tension and dichotomy between his love for the arcane and a girl which was present in his old lore champion judgment.

It hasn't been thought out yet

Urgot sat on it.

And it broke.

Cuz he's fat.