I’ve merged in a thread here.
Upthread there is a huge amount of data testing the proposition of whether starting boards are random, and whether there is a link between the color of heroes you bring and the color of tiles. Based on large datasets, gathered from sequential raids, there is no evidence of bias in starting boards.
@Garanwyn is also collected data here:
Color Stacking Fairness Project
Furthermore, the lead designer has told us bluntly that boards are random:
”The door of a bigoted mind opens outwards so that the only result of the pressure of facts upon it is to close it more snugly”
—Ogden Nash