And if the Blades underestimated the Thalmor, the Empire should have been doing their own espionage. You said the Penitus Oculatus was also looking into the Dominion, and apparantly they too also failed to report any plans of invasion. And the Oculatus is an Imperial organization through and through.
The Empire was doing their own espionage, considered them a great threat to Imperial security. Almost went to war with them (Which would have been a huge mistake at the time, since it was wanted as a diversion).
The Thalmor are clever, no one saw the Great War coming. Now you could blame the Empire, the Blades, the Penitus Oculatus. Or you could just accept that the Thalmor are crafty. I doubt the Dominion were very open about their intentions, they were plotting this for one hundred and fifty years. Maybe their plans were discovered and the great purge wiped out anyone who could warn the Empire.
Either way, a growing superpower, with extremist views who share a border with you and have been picking away at your territory for over a century, and you weren't preparing for military action?
They did have some defenses, but how long do you sit around with your army on their border? One hundred and fifty years? You prepare for Military action when intelligence reports it is needed. The Thalmor picked away at Valenwood, and then went silent. Elsweyr wasn't part of the Empire for a long time when they joined the Dominion as client states.
The Empire's power rises and falls constantly. One Emperor could have a very strong army, but then two crowns later and recruitment has dropped to where you have Military weakness. What if people decided they didn't want to join the army in your country, time goes by and current soldiers retire or decide to leave the Military for a civilian job. But, no one has replaced them.
Will you blame your leader? "You should have conscripted people by force!"
The Dominion have a well trained Military, they had the advantage of surprise. The Empire managed to survive against all odds, so give them some credit.
I'd say that the lore in Daggerfall is underdeveloped, because Talos would probably be at least acknowledged, even if he's not worshipped. Still, it's in game stuff so I'll have to let you have this one.
A lot more rich in lore. Before Bethesda starting "dumbing" things down. Also Bethesda's TES lore comes from a source the creators put together in the 90s. There is still large amounts of stuff unused, it isn't underdeveloped. Be like saying Skyrim's lore is. Arena was, back then they had no idea what an Elder Scroll is.
Akatosh is still not popular in Skyrim, the Solitude temple has a shrine but that's it, other than the odd one you'll find out in the wild. One of the in-game books explains that because of the dragons and Alduin, along Akatosh being Auriel, made him pretty unpopular.
The Nords preferred the Dragon Ysmir, to Akatosh over two hundred years ago. Back when they were resisting the divines. Though you still have many Divines not being popular by the traditional Nords.
The Empire endorsed Talos as a divine and there is overwhelming evidence that he became a god.
Of course there is. The Empire still worships Talos, they're just silent about it at the moment. The Mede Dynasty tried very hard to preserve Talos' Empire. But, sacrifices have to be made. Open Talos worship vs millions of lives.
Most religion is about sacrifice.
I'm just saying it was a low blow of the empire to give last rites to their prisoners that went blatantly against their religion. Yes, everybody gets touchy about religion but to do that to people who are about to be executed is just sad.
Arkay's Rites is not against their religion. I doubt that Stormcloak was so offended over "Eight Divines" as he was bored standing around. He wanted them to get it over with, cause the Empire takes their time.
Saying the Eight, isn't going to offend them. Or should I condemn any Nord who says Kyne? Because that is offensive to the Imperial religion Eight and Nine.
There is a Stormcloak Jarl who doesn't worship Talos, or consider him a God. She worships the Eight Divines. Should she be taken out back and burned because she is blatantly against their religion?
The heresy isn't confirmed, it's possible the truth contains elements of both. Just because he went by the name Hjalti doesn't mean anything. The orthodox story never gives him a birth name, he is named Talos for using the thu'um, and then makes up Tiber Septim for being Emporer.
The ghost also confirms High Rock. The orthodox claims he was born Talos of Atmora.
For anything not in the Divines, yes cults are the norm. But the city chapels and churches, that sort of stuff in the more civilized parts of Tamriel (and presumably a large part of the population) is more mainstream than cults and that.
The Imperial Cult is the Divines, and the chapels and churches. Civilized parts of Tamriel? They're still fanatics, with religious Military orders for each of the Divines. The Talos Cult has large numbers within the Legion itself. Tiber also formed the Cult of Emperor Zero.
The Moth Priests and their Cult is interesting. They once rebelled against Tiber, he lost the Imperial City to them for awhile until the Third Legion had to retake it. Such is with Emperors and being forced out of their capital?
All the more reason for a trial in Cyrodiil
Okay. Could you elaborate how we get Ulfric to Cyrodiil? Pale Pass is blocked.
I wonder if the Thalmor actually had something to do with that... Only crossed my mind now, they did get to Helgan ahead of Tullius.