That data is not include bonus +3 upgrade from Hoard Quailty. So if you’re clearing all room in maxed out Factions, you expect around Delve Chest Level 7.
Thanks for the kind word, Cyrup! 
I actually have that map screenshot just as a reference for number of rooms in each Factions. But got an idea and try to put the Legendary troop’s art in for fun. It looks more unique that way. So I also included that number line to make it more informative. ^^
No, it didn’t appear to work that way. All room of each rarity can be any room of it matching type, except Treasure Room. Tower of Doom also seems to work this way.
Although, there is one problem I didn’t work out yet. “Garanteed Treasure Room” is separated from the rest, so it’s easy to calculate, but there is also “Potential Treasure Room” as well. I didn’t fully know how it work yet, and dued to its unusual appearance, it’s hard to pinpoint where they are at each Factions as well, if they did existed there.
My guess right now for how it work is it will replace the room of matching rarity. For example, Cedric’s Hideaway in some normal Rare room, or Dragon Fountain in normal Epic room. That 2 rooms on the right side of The Warrens could be this type. Overall though, it shouldn’t affect overall statistic that much, as they’re quite rare.
Also, per Shimrra’s request…
