You seem to be missing the point -- you are trying to complicate something that isn't complicated. Taking away items of stuff like Kyogre and Groudon wouldn't change their power. It might make them slightly weaker but they are already so far gone that it wouldn't matter.
Well then let's just ban everything but Burn Orb on those two and test them in OU for a couple months, you can't argue that their overall strength goes down significantly to the point where they
could be viable in OU. And hey, what about Deoxys-D without leftovers, that would be interesting right? In fact, I wouldn't be surprised if we could bring down the entire Uber tier, and just muck with item options until the "OU" tier rests at around 40 or 50, with 0 or very very very few bans. Hell, why leave it at that, why not make all of our UU troubles go away and make
that ruleset filled with stuff like "No Slaking with attack-boosting items"? Doesn't exactly have a nice ring to it but it could sure balance things out right?
In fact, why stop at items? As far as I'm concerned, you have no justification for banning Yache Berry on Garchomp that wouldn't also allow us to ban, say, Earthquake or Outrage on Garchomp. Do you have any, or was this entire proposition thrown together on the basis that "the primary argument for Garchomp becoming Uber has been Yache Berry"?
I don't think I'm "needlessly complicating" anything at all, the very nature of your proposition is extremely complicated all on its own. We ban Garchomp or we don't, any middle ground does not, in my mind, do anything to simplify the rules, and in fact only serves to complicate them. Honestly I think jrrrrrrr misunderstood the second part of the AA post he quoted, or otherwise neglected it; either way it's something we definitely should be taking into account here.
Like jrrrrrrr was saying -- we are trying to make the most balanced environment possible. Testing after testing if we could prove that one of those pokemon without a certain item could make it in OU then we are obligated to make that a reality.
1) This process would take a ridiculous amount of time. We could probably come up with a way for every single uber to be usable in a diverse, balanced OU metagame, if we did enough testing with different pokemon/item combinations. Just based on the amount of time it would take alone, such a process would never be worth it.
2) This process could overcomplicate the ruleset so much that even saying "well... at least it's more balanced now, right guys?" probably wouldn't justify it.
3) Smogon is
not trying to create the most balanced environment possible, which is something I'd think should be obvious considering that Deoxys-S, the widely-renowned "best late game cleaner in the game" is now OU, and that (!) Garchomp, by far the #1 threat in standard, is still heavily under question.
While there is no proof that Yache exclusively makes Garchomp uber (although I don't think it's uber anyway) Yache is pretty much the foundation of all the arguments making Garchomp uber. Can you come up with an argument for Garchomp to be uber without Yache? If not, then it should be safe to say that by removing Yache we are making Garchomp fair in OU.
I don't really care how balanced Yache-less Garchomp is any more than I do about Swords Dance-less Garchomp, both are hypothetical scenarios that do not, and should never exist unless Gamefreak decides to do us a favor and remove it in-game.