Better informed force is not a larger force. The thalmor used tactics, subterfuge, and gathered intel. Whereas the Empire just went in blindly. It wasn't mede that saved the empire, it was Decianus completely unintentionally. Because of the "invalids" he left at hammerfell, the force at IC thought they'd only be facing 2 legions. Intel and tactics are extremely important in war.
That's probably true, better intel was necessary, and the Penitus Oculatus should've been on it like they had in the past (Didn't e en realize that every Blade in Valenwood was dead til their heads were delivered

). Still, it's a superior force not by numbers but in intelligence and tactics, like you mentioned. They are also elite troops well trained in the arcane as well.
By the time of Red Ring, the men in those counties you said were fleeing were already dead. The thalmor had swept through that area long before the concordat, and the thalmor don't take civilian prisoners.
Does it really say somewhere that there were 0 survivors from any of the southern counties? Seems ify to me. And, had the war continued, all other civilians would have suffered the same fate if the Dominion had slaughtered every person in the southern counties.
And saying Ulfric demanded talos worship in markarth is a bit of a stretch. The jarl of Markarth said if he retook the city for him, he'd allow it.(This is probably where the thalmor influence came from) The empire gave the go ahead on it too. Ulfric takes the city back, the thalmor protest, and the empire has Ulfric jailed instead. You think that might have made him a bit bitter?
If that's the case, the Jarl didn't have the authority to override Imperial treaty like that anyways. And the Empire was more or less forced to grant Ulfric's request of reward because the city was in utter chaos. It's like a police force saying, "We won't be enforcing the law until we get all we want.". Since he practically blackmailed them into getting his way, and may have committed war crimes against the people of Markarth, it may have been he deserved that jail time.
The nords are the reason the empire exists in the first place. If the empire doesn't want to look out for their best interests, its in their best interest to look after themselves.
It's a two way street I think. The
rest of the Empire doesn't like this treaty either, but they've got to put up with it for now.
And this is the big issue I have with the empire. The empire is not just Cyrodiil. Mede did not have his subjects interests in mind, just cyrodiil's.(And even then I think he just really didn't want to lose IC hence why he surrendered only after he had kicked them out of IC)
Your right, it's not just Cyrodiil. Its Cyrodiil, High Rock, and (tenuously) Skyrim for now. Cyrodiil was the area under attack at the time, therefore it was the priority (I know, Hammerfell as well, but that was handled luckily through the invalids). I can't tell you what Mede would have done had the situations been reversed, only what he should have done.