I got Angel Jin for like 5 hours Straight of running Arcade Mode Easy with Devil Jin(Worst Final Boss to get, can combo everything/your HP Bar below half after 1 hit, always rage arts, and is good at blocking/tp'ing through hits for grabs to combo strings) and only got Azazel once, and Devil/True Devil Kazuya 0 times.

I originally thought this had to do with Finishing Story Mode, but apparently my friend whose finished story mode but never touched ranked/arcade quest has only gotten Devil Kazuya in his Arcade Runs. My other friend whose played as much ranked/arcade quest as I have was also only getting Angel Jin for Hours as well as more difficult AI in arcade Easy

From a quick internet search it seems related to both completing Story Mode and getting an amount of perfects in your run.

• 1 Perfect = Azazel
• 2 Perfect = True Devil Kazuya
• 3+ Perfects = Angel Jin

So if Angel Jin is that much more of a time loss (I haven't done Story and haven't tried to fight him) then it's probably optimal to do runs on an account/profile that never beat Story Mode if this is indeed the case.

Watching my Arcade (Easy) Devil Jin Run after hearing/learning that is hilarious, over half my rounds it almost looks like i took damage/baited attacks intentionally to not get perfects lmfaooo