Onett is way too homothuggish just like the Space Animals.
If you think corneria is a terrible stage because of camping as well as I do start banning corneria, I think OC stages are too good for tournies. There's no reason to take anyone to MC or Brinstar with peach in my opinion it's a pointless thing unless you win the first match really, even then I doubt it would be necessary. I play peach I don't even like taking people to those stages. I only take eddie there because he will never play me with anything but his fox normally and he sucks there. I see no reason for there not to just be neutral 6 tournies all the time. The game is not called super counterpicking bros. melee. The MW was known for our PF counterpickers back in the day, this is not true anymore. I guess some people like those stages though and would be upset for their non auto win stages in the 2nd game of a set, because we all know that second game is just oh so crucial when you get three stocked the first game on a neutral stage.
I mean I know it's your tourny and your rules and I know you play sheik for the most part so you have no bias for that stage to be on. It's just your opinion about space animals needing more in their favor that baffles me. I mean they have the speed and the one frame moves. Do they really need that stage where they can get an upsmash kill at 80%? I guess so. I mean I would love for you to put Peach's Castle on because I like that stage it's not gonna happen though. That stage is also a good counterpick for space animals. Why not add that one as well or just add that one? Why does it have to be onett? It just seems to me that stage advantages aren't that big of a deal. Stage disadvantages are a big deal, for example gauntlet that MW went to, everyone Tink played took him to a certain bad fox stage and almost everyone he played beat him, in my opinion that should not happen but, it is still not a big enough reason to ban a stage. It's kind of like saying I'm going to ban Mute City and Brinstar just because they are good Peach stages and Peach has too many good stages. I can see banning Brinstar for the same reason Onett and Pipes are banned just switch fox/falco to peach for the reason. I have never and will never view Mute City an instant win stage for anybody it is good for Peach and Jiggs because of the large sides and recovery because they do not need a ledge that is all. It is also good for fox though he can shine people right off the ledge with no edge to grab and doesnt really need an edge since he recovers so fast from his up b. Brinstar sure is way too good for Peach but, I still don't know about banning it because there are ways around not getting destroyed by her simple strategies there.
As far as your list of Peach counterpicks goes you are most definitely wrong, no offense. For I would say Japes is a good Marth stage before it is a good Peach stage. All Peach has at Japes is a high ceiling. DK64 is somewhat good for Peach, she can survive a long time there but, she also has a pretty hard time killing there, for the stage allows characters such as fox and falco to go to the upper platform or to the ledge. In this situation, Peach lacks the speed to get up to the upper platform or down to the ledge after fox or falco make their decision on where to go, so it is a situation in which you have to read your opponent to get the kill .
In the end, I say that there are only three peach stages good enough to be considered her counterpicks and those are Mute City, Brinstar, and DL64. Space animals on the other hand can counterpick basically anywhere but those 3 stages and have a much better chance of winning then Peach or basically any other character would. As I said before I completely understand that you are not biased and that what you have is what you truly think. You might think I'm biased because I play peach. The truth is I'm just posting my opinion and what I think on the subject. Playing Peach and watching other people play Peach I would assume would give me better knowledge of her good and bad stages. Also, seeing people play fox and falco and knowing and speaking to people who play Fox and Falco, gives me some knowledge on their good stages as well. Now I have no idea if fellow Peach players would agree with me on this or not but, I post in full confidence that the majority of the veteran smashers would agree with me on Onett being a banned stage.