Put it this way, I botted season 1 para 1-502. I quit at 502 and went back to non season where I was around para 620 and botted almost non stop 24/7 running rifts(common, stupidly my mistake, full is best exp + drops). It took months to just break para 850, and I only got barely 7 levels from my seasonal roll over 1-502 lvl while in the 880s. I got banned just over 920+, where its about 38b per level. I restarted a character, friend PL'd him to 70 and gave me a ancient nat weapon, mara set, royal ring, and im already paragon 300 with less then 24 hours played on my new DH. Found a gift, ancient WH 5/50 640dex etc, rucksack, few other good items. Nothing special, but I can use turbohud or calculate manually and see that speed running t6 full rift clears I get about 3b exp/hr, Now my old pre ban DH using the same fire multishot cindercoat build with a 3.3k ancient kridershot and ~60% RCR(30 was from fire cinder) only got max of 3.5b exp/hr with pools. So imagine 3-4b an hour, and it takes between 30-40b per level.
I also had a raekors barb, He got similar exp/hr however, if it was a bad map the exp could drop really low. If it were a wide open map with no turns or blocking, A raekor barb can get 4-5b an hr+ easy just straight charging through EVERYTHING(disable gold pickup, pickup nothing but legendary or imperial gems. otherwise he can charge from one side of the map to the other THEN walk back and pickup all the non legendary items ie gems/craft mats he didn't get cause he was in combat) before finally walking back to the next level, or whatever.
Obviously bot exp will always be less per hr then by hand, but a bot can keep going after a person is worn out from rifting for 12 hours straight. I think what blizzard did was essentially turn warden on to scan for bots for lets say a week, at the start or just a few weeks into season 1, then stopped, and possibly turned it on every few weeks again to catch people and flag them. Then the massive banwave hit, That way theres no suspicion of is X DB ver detected etc etc. Because it most likely isn't, they simply saw you on 24/7 repeating nonstop over with obvious bot like movements.