Johan once summed up the reason IR failed as "lack of content."
I think this perception is wrong.
The real reason IR failed is that "AI cannot create a world map like the historical one."
In other words, we were disappointed that AI Rome did not conquer the Mediterranean world.
We must not repeat this mistake with Caesar.
In other words,
・AI Ottoman must expand into the Eastern Mediterranean.
・AI Britain, AI France, AI Spain, and AI Portugal must create colonies all over the world.
・In the first place, AI Spain must be established with a probability of more than 80%.
・AI Persia and AI Mughal must be established.
・It is desirable for AI China to be unified by some force.
・Of course, there may be times when AI China and AI India are split, but that should not be the case all the time.
We want a solid AI nation to grow, not a world divided into small pieces.
Partly agree, I think the core of what you are describing
is the lack of content that Johan saw in IR.
Contrary to what many forum users think, EU5 can't be a perfect simulation of the entire universe down to the atoms, its simulation aspect clearly has limits in its scope (and I am calling it now: Vicky3 will always have a deeper societal simulation than EU5).
Unique content around historical outcomes like all the points you said will remedy this by making the game varied by region and giving us unique challenges based on things that actually happened.
But for a piece of historical content to be likely to appear, an earlier piece of content needs to "nudge" (not railroad) the game in that direction. Like the Western Schism raising Catholicism's reform desire, thus making the Reformation more likely to succeed, thus making the League Wars more likely to appear. This enriches the game.
If we won't have enough of this kind of content (including late game content) we will criticize the game for being bland at launch and for all countries feeling the same, which is the exact reaction Vicky3 and Imperator Rome got too.
Imperator Rome could never solve this issue by introducing more content, because on the one hand it is an EU spinoff and its simulation is not as deep as Vicky3 (it's too mana focused), so it couldn't enrich the experience with deeper aspects of the simulation without completely redesigning itself, and on the other hand most countries in IR are unrecognizable today and the only historical narrative we have from that period that can turn into new content is Rome conquering everything. They could make more content that is only for Rome, but I imagine they wanted the game to still feel balanced and not have Rome stomp everyone each time.
Hence why IR remained a bland game, too mana-intensive to reform and stuck in a period without narratives to give to most countries. I believe this is the lesson Johan learned from IR when he designed EU5.
In my opinion IR would have been better off as a game where you play as a character
in Rome. Make the game about managing your patrician family and network, and give Rome all the content and narratives it needs while it conquers the known world or fails to do so by your hand. Then, perhaps, we would have gotten DLCs to play in places like Carthage with a similar depth.