So, I'm failing to see how the wizard wins in any conventional sense. What you've been describing is a super powerful mage who has pulled himself away from the world into his invulnerable fortress of solitude guarded by his infinite guards and magical effects but you've yet to present any reason why he would ever be attacked. By making this character so isolated he's essentially closed himself off to any reason for attack. Why does the wizard ever leave his plane? Does he need to, it seems like he'd be pretty self-sufficient on his own.
DM: Alright, there's an almost omnipotent and omniscient wizard, guarded by impenetrable defenses on his own demiplane of terror and magical might.
Players: Okay, what has he done?
DM: Well nothing but he's really powerful so he could destroy the planes if he wanted!
Players: Well does he want to?
DM: Well no but...
Players: So than there's no really reason to go confront him?
It doesn't matter. The hypothetical situation is there is a mage, and a non-mage who wants to kill him. It doesn't matter why. If we don't go on that assumption, we have nothing to discuss.
Also, as I outlined before, the mage has
plenty of ways to influence the world without actually physically leaving his demiplane. He can summon/call/create/permanently enslave powerful minions, and send them out into the world to do his bidding, or he can travel himself in the relative safety of an Astral Projection.
So you're angry that within game a deity would block an ever-increasingly powerful wizard? I don't know any game, any game, where the DM wouldn't eventually stop the use of CoP (even in the manner as described above because hey, it's both a lot more flavorful than just banning it out right and can actually bring something into the plot) when confronted with a TO-wizard who spams CoP as much as possible. You may cite it as DM Fiat but that's exactly why it's there, to control the guy your presenting.
I don't disagree with that at all. Of course the spell is fucking broken. That's the whole point of bringing it up all the time. The spell is so fucking broken that if you use it as written, the goddamned wizard is untouchable.
It's not the only one, either. It is one of the most powerful spells he has access to, but there are a crapton of ricockulously overpowered spells right there in the core books, and it only gets worse if you allow more sources. So if we're talking about "is there any way, within the actual RAW, for a non-caster to beat a paranoid wizard who uses combinations of the most powerful spells in the books in the most optimal way", the answer is "no, because his spells are way too fucking overpowered to ever actually get used in a game like that".
What angers me is when people say "Eh, wizards aren't that tough", and then every example they try to use to prove it involves them ignoring/nerfing the rules somehow, or relies on the DM limiting the wizard's spells in some way that isn't explicitly spelled out in the books*. You know what that means? You lost the fucking argument, and just can't admit it. Wizards are stupidly overpowered when played to the maximum of their capacity, and unless you houserule them or their players restrain themselves, non-casters have zero chance of ever taking one down, except in extremely rare exceptions (and even those can probably beaten by the wizard with enough cheese).
That was the entire premise behind the long, three-thread series on discussing, building, and then trying to take down powerful wizard builds. There were a few ideas that could certainly take down many wizards, and I think even one or two ways people came up with that might take on the most insane wizard. (Using the Breaching Obelisk to crash into his demiplane, and something else... I forget.) No one ever actually put up a build and said "Ok, that's it. Let's throw down", though. There are several wizard builds there. You can go look at their stats, and build your guy specifically to take them down. There is no wishy-washy TO changing the wizards abilities around to fit the new challenger. They'll be ran exactly as is. Go for it. I'd love to see someone succeed. No one has even tried yet.
*
the rules don't tell you under what circumstances COP doesn't work, and so it is totally up to DM whim, which should be excluded in these kinds of arguments