The idea I had posted in the discord a while back was that Arena of the Valkyrie was literally that - as a reference to the
classic sci fi short Arena, by Fredric Brown, a mysterious figure (the Gamesman) promises control of his Wellsprings to those whose armies can best each other in his games. His "games" would be the scenarios, and the figures in the set would be the units sent by each general to try and claim some of the glory.
Just a random idea, take it or leave it.