Man these bots are ruining things everywhere. And the biggest disadvantage is that they keep getting smarter and more powerful every day. More resources they get, bigger nuisance they become. Wherever there is money to be made, you will find bots.
Maybe having some sort of complex captcha after every few matches might help. But then again, it will affect User Experience negatively.
But I do agree banning bots is the right thing. Even if goes against decentralization. At one point you have to choose between a few bad actors who just take or real players which bring the actual value to the game.
Just giving a stern message that if found, then bot accounts will be banned and their cards be burnt (removed from circulation); will do a big help.
I would like to put here the example of EOS Knights. Both are of course different games, on different blockchains; but both Steem Monsters and EOSKnights are top played games (keeping aside gambling games) on their respective blockchains. Now, this EOSknights is totally against bots. Their community and devs. If bots are found, they are removed along with their items. Plus, they have a bounty programme to extend their reach.
Steem Monsters can also launch such bounty programme for bugs, bots or other vulnerabilities in game. It will definitely be cheaper than wasting rewards on bots and making real players a bit angry as seen in comments. Plus, a bounty programme will encourage even those devs to contribute who normally don't play Steem Monsters. I will suggest talking to Lukestones as he has made some tools for EOSknights. He might have some ideas.
I do however agree that rewards are more than enough even after rebalance. I haven't seen any other crypto game dishing out so many free rewards. But ya, we can't afford to keep lowering them after every season, especially for the lower tiers.