Categories have their own reward share, so it's not unfair if a contribution in that category doesn't get upvoted because other contributions in that category have a higher score. It simply means that the author of the contribution with the low score should try to up the quality of their contributions. Luck has nothing to do with it.

The fact that contributions with a low score get upvoted simply because there aren't any other contributions in the category is not a problem with the bot.

Finally, the queue is sorted by creation date and then by score. This means that contributions when contributions in the same category have the same score, older ones will be prioritised.