When you begin to think about what such an "ideal environment" actually means, some of the problems with event moves and a simulator begin to come to light.
Let's suppose that today there still exists a 31/31/31/31/31/31 ideal nature Wish Blissey in somebody's possession, and there is provenance to indicate it actually came from the event. However, the person who has this Blissey is selfish and does not redistribute it. We know this pokemon exists, but you can't just go get it and add it to your team because this guy just won't let you. So what exactly are we "simulating" by allowing it?
The pokemon did exist. So we're using a simulator to cover up the fact that someone's being a douchebag and keeping a perfectly legitimate event move pokemon to themselves. So to answer your question, we're "simulating" a pokemon that was legitimately released by Nintendo and intended for our use and enjoyment. As you say below, you do not object to the process of cloning, so in an "ideal" world, everyone would have access to said Wish Blissey.
Or consider this. Suppose that that he was willing to start distributing it, but then by fluke his file was erased. The pokemon doesn't exist anymore, so there's no way you can get it onto your team. Again, what would be "simulating" by allowing this pokemon when there is no way you can actually get it onto your team?
Again, this would not be the ideal.
The only self-consistent way I can see to allowing event moves is to designate one person a trustee of event moves and have this person collect clones (which are legal because we can get them through an ingame method) of all trusted event moves and distribute them to people who request them, and also has a backup of his file. Of course, this is wholly impractical, so it's simpler just to ban event moves. Or you can adopt an inconsistent position.
Or, in the case of the ideal metagame, we can just assume this would be the process, and simulate it. A simulator should simulate the best-case scenario of what's possible (if you argue against this, you're also committing yourself to argue that the Modest 31/31/31/31/31/31 Heatran on my Shoddy team at the moment should not exist either, because no one that any of us know of has actually obtained one in-game). So this argument really doesn't work, as for the purposes of simulation, one can just
assume their way past all the impracticalities, much as they can assume their way past the fact that no one has actually obtained a 31/31/31/31/31/31 Heatran.
For any extremely unlikely IV-Nature combination on a breedable/legendary pokemon, there exists an algorithm you can follow to get the pokemon.
1. Breed for the pokemon (or soft reset and catch or whatever).
2. Check the IVs and Nature.
3. If they are unacceptable, return to 1.
For some combinations, this algorithm may take a very long time, but it will always get you your pokemon eventually, assuming it is legal. For event move pokemon, there is no such algorithm you can follow. (Even the ones that involve items that allow you to soft reset do not meet the criteria because the item can be lost through files being erased as well as other concerns I have outlined. For these events though those concerns are a lot less important and less relevant.)
Surely, even you must realize how flawed this is. Just because you flip an infinite number of coins does
not mean that at least one of them is bound to be heads and at least one is bound to be tails. The chance of
each coin flip being heads or tails is still 50%, regardless of what the flips before and after it may be. There is an infinitely small (but still plausible) probability that there will be no heads, or that there will be no tails. By the same token, it is entirely plausible that if I were to reset my game an infinite number of times, I would
never obtain a perfect Heatran. So by your logic we should ban all pokemon with all IV spreads, as there's a very real chance you may never obtain them. So let's never play pokemon again.
Just for clarification's sake, a lot of your post seems to revolve around items/files being lost, someone being selfish, and other aspects of human error or human flaws. For a simulator, in which the so-called perfect environment is being simulated, these are largely irrelevant.