The AI cannot play arena, unless you make a config file for each deck you create. This brawl is even worse, since you have to deal with a plethora of new cards, and I doubt HR can deal with.
HR was made to get gold and rank up, and I doubt spending the time making an optimised arena feature would pay off when you could optimise the actual role of the bot instead, which is to win ranked games.

Stick to wild casual/ranked. Dont use it for anything else.