I received an Arcane and two Celestial stones tonight with my pvp battles. I think I did 25 or 30 battles but did not keep track. I will tomorrow night though and repost. The rest were probably around the normal difficulty numbers.
I’ve found all difficulties to give about the same. I was running Warlord 3 to farm a non-pvp match a couple 100 times from a kingdom that I need its epic traitstone and got seemingly the same drop rates as hard on pvp. I didn’t keep track of all stones accumulated, but from those 100ish I only got 1 epic and 1 legendary traitstone.
It was decently fun. Each match was only 1-3 minutes, so it went pretty quick. True Shot just one shots everything in most AI matches, particularly that of Khetar. Precious Karakoth traitstones can be obtained here for an attempt at +1 magic.
Have it with +2 purple banner for a total of +3 purple. Every purple surge puts skeleton to full. Each Skeleton cast kills 1-2 and each Bone Dragon 3-4. Any magic linking troop can be last slot. Any true shot troop can be first slot, but Glade Warden is the tankiest of them plus has some board manipulation.
Yes - you can get traitstones from Challenges. From memory, I played about 50 battles in Whitehelm to get the Arcane Summer Traitstone which my Centaur needed for his third trait (True Shot).
I usually take a double-valkyrie & celestial approach to ensure I get 100 souls per match also. First & last characters change depending on the kingdom the battle is taking place, but normally a traited serpent or traited Gryphon will be in position 1 as they help mana-up the valkyrie.
So as far as drop rates I didn’t track the other stuff and I don’t know how many battles total if anybody does off hand but I completed quest lines for pans vale, maugrin woods, khaziel, khetar, forst of thorns, zhul’kari since the 1.08 change. I received 3 celestial from doing those. Lots of major and minor runic and some arcane. I’d guess 20ish fights per kingdom but I don’t know exact numbers. Difficulty setting was hard.