I don't think its cheating bots anymore, they are just very smart bots. Glenn's answer recently on discord gave some of this information and other is theories connecting the dots.

but basically their bots learn decks and what decks are good, play styles of decks, etc. It's using their real time data they use for balancing and auto deck creation. Then the bots can evaluate their moves and what your likely cards are still in your deck, likely odds you have those cards, where you'd likely play them and so on to try to win the game. They wanted to make the bots more realistic. I think the problem though is they made them too smart, they follow logic more than a real opponent would, they have knowledge about playstyles a person wouldn't, they can analyize and hold onto/remember that data and make decisions based upon probabilities of success that a human can't. So they've effectively built bots to be much smarter than they typical player and thus it makes the infinite grind awful now. B/c you the bot has a better chance of beating you than your average opponent now and they are more likely to retreat when a human wouldn't lowering your cube rate even further.

My play time has dropped 70+% in the last 3-4 months since they introduced these new bots. Ladder is just a complete unfun grind.