If the tools I have in mind were in place, I would be able to name you a hundred equivalent or better for every one you can name. The reason you do not want to admit to this is either because A. You lack the gaming experience to comprehend, or B. the reasons I listed up above in previous posts.
I guarantee you with the right tools, I could obliterate any game scenario your imagination could come up with. 100% guaranteed. Not a single doubt in my mind.
No, you could not.... As 99% of all mods are poorly made, extremely poorly
balanced flights of fancy by the mod creator. Just look at civ4; The vast majority of mods are simply kitchen sink mods, attempting to throw in every possible unit/resource/civ/leader/whatever without any regard for how they
work together. Without a cohesive structure, the mod loses any point. It is interesting for a few games out of novelty, after which the imbalances become noticeable and it loses the fun it had.
The simple fact is that most players are not actually good designers; The vast majority of suggestions I've seen for new Civ5 civs, for example, sound awesome... For the player. As an enemy, you would find them horribly broken. That type of design is innately flawed.
As for coming up with things my imagination could not dream of... That's hogwash, particularly as you seem to have an interest in creating simple scenarios based on actual history. First off, scenarios are never as complex; You could create new mechanics I wouldn't think of, but a scenario making use of existing mechanics? It'll hold my attention for at most one game. Second off, you're working
out of history; Something anyone who wants to become a game designer (read: me) should be very well acquainted with!
That is entirely irrelevant, however. I've made my point. If you don't believe me, why don't you go back and look at Little Big Planet, or any of the Elder Scrolls games, or Civ4, or any other moddable game. Look at the sheer volume of mods available. Then look at how many players have played each one.
Quality matters, even in games where it is simple for everyone to create content. Your "Modding Utopia" is exactly like all other utopias; A pipedream that fails to account for the whole picture.