In the past when a new set was released I'm fairly sure it was possible (at least sometimes) to specify that one wanted to play a bot game with extra cards from the set. It's the method that I used to use to become familiar with the cards from new sets. Unless I'm overlooking it, such an option doesn't seem to be available for Allies. My suggestion is that it should be resurrected for future new sets (or made more obvious, i.e. as an option in 'Bot Game', if it does exist and I'm overlooking it).
It's still possible, you just can't do it from the automatch screen. Open a table, add a bot and make sure the "Extra Allies" slider is to the right:
(https://i.imgur.com/7Zmn4hh.png)
Thanks. I should probably have thought to look at the Tables option, but in the past I've only ever used it to look at a previous game.