The side blastzones are seriously not close. I actually have experience on this stage, and I can say with absolute confidence that in the 99% of matchups where chaingrabs into the wall are not a factor, you tend to actually stick around more than average. If anything, argue the stage is too big and campy since it is indeed big and campy (though nothing extreme). Calling it small is just bizarre. I suppose the side blast zones are close to the ground in the sense that it's a walk-off, but time has demonstrated over and over again that camping a walk-off to back throw is an incredibly risky tactic that isn't broken at all, especially not on Onett where the cars frequently dislodge you from such a position.
The ceiling is a HIGH ceiling. This is something I can trivially prove, in fact.
http://www.smashboards.com/showthread.php?t=156908
Onett has an objective ceiling height of 88 on this scale (Mario killed by other Mario fully charged usmash in training mode). Final Destination, Smashville, Battlefield, and a ton of other stages that have the "normal" ceiling height have a value of 82. The only stages actually on the list (which does ignore a few stages like Mario Bros.) that have a higher ceiling are Green Hill Zone (89 from the VERY bottom), Summit, Jungle Japes, and New Pork City. In other words, Onett is a stone's throw away from being huge...
The thing with Onett is that it's easily the most fair stage on which you could claim King Dedede (who is really the only guy who is actually THAT bad with walls and walk-offs) gives a great deal of grief. It's only about half of the matchups involving him anyway (the other half are either matchups in which he can't really chainthrow or he was pretty much going to win on any stage). Then you consider the cars saving you from chainthrows and how you can play strategically around them; at worst, I can really only see it being reasonable at all to complain about playing on this stage against a legitimate King Dedede main, not just some random guy CPing King Dedede to "punish" you. So, if you are up against one of the actual King Dedede mains, you could just use a personal stage ban if you're using that half of the cast against him. Then we have an extra legal stage and a very good one at that. It actually was legal around here for a bit, and it was bizarre when it was banned because it had never caused any problems but was just banned for speculation over brokenness it was claimed to have. That didn't sit well with me...
The idea of calling tactics "cheap" strikes me as absurd. Why is strategically ducking around the houses somehow worse than how you play to win on other stages? You can SDI out of dtilt wall combos which are really hard to set up against someone trying to avoid them anyway. I don't even understand a claim like "disrupts combos" because this game is just not about combos. It's about pressure and bad situations, and stage geography is a part of that for the attacker and the defender always so why is it somehow "disrupted" on Onett as though it had a natural state to begin with?
Also, if your philosophy over stages judges 90% of the stages to be bad, I really don't think it's a good philosophy. The standard for stages is the stages that exist; why would you base your stage standard off something that isn't a part of the game itself? I love how in Brawl every stage is unique and different with a majority of them being legitimately fair. Sure there are a lot of stage specific tactics and such in Brawl because of it, but since we are playing the game and not designing it, shouldn't we accept and embrace that?
I want to be clear again that my opinions on Onett are based largely around my actual play on Onett, not theorycrafting. A lot of the bizarre claims against Onett (like calling it small) make me suspect that some of the argument against it comes from people who haven't played it extensively and actually experienced the things they are complaining about to be sure that it is really representative of the best tactics on Onett. I know this is fruitless in the end since too many people simply hate the stage and won't be moved, but I think I'm legitimate to expect the objective facts to line up and for arguments against the stage to be backed by experience.