There have been multiple discussions on this very topic, all of which disagree with you on that point.
The only people it is fair to are the one who also hide, it is unfair to the 99% other players who keep their best bot in the arena during the whole contest.
You can train against them, they can't train against you. How can you think this is fair ?
I understand why you do that as it provides a real advantage and you're clearly here to win (I respect that), but that's a really lame way to win imo (cf. my sucker punch reference in the PM topic).
Also, don't forget that the prerequisite for you to win contest by hiding is that some people among the top play the "legit" game and push their AI so you can train against them.
"Do the same" will you say. This is clearly not what this platform has been designed for. Imagine if everyone does this... How sad.
As for the solution, it's already been proposed to do the same as other platform, make every IDE play public, so that if someone train against your bot in the arena, you can watch the replays.
EDIT : Also crying about the unfairness of the multi ranking on CSB while abusing the very same system in contests is kind of funny imo
EDIT 2 : To clarify : If your definition of fair is that everyone can do it, then yes it's fair (my definition differs a bit).
But unless CG fixes the issue, the fact that hiding becomes more and more common is an incentive to hide for everyone.
As a result, contests will become offline-self-training contests and the level of the competition will significantly drop, which is the opposite of what you seem to cherish.
I'm not blaming you, I'm just sad that you're promoting something that could endanger the quality of contests as we currently know them, as CG will most likely never fix this issue.