And right now, there's nothing to do but for him to be in Skyrim. If the Dominion or Empire were to attack each other, then recall him. There's no proof he's the best the Empire has either.
No one said he was the best the Empire has, but he's the Emperor's go-to General for restoring order. Tullius himself mentions he's often sent to places that need fixing.
An invasion of Alinor by the Stormcloaks would fail, but so would a Dominion invasion of Skyrim. Not a long term solution by any means but it's not like the Thalmor are being overthrown anytime soon anyway.
The Dominion can't invade Skyrim, the Empire is blocking them. The Thalmor however, will make your life as hard as possible. Which is what Ulfric fears, them turning greater attention to Skyrim.
I sure hope they don't go to war right away. Let's say the Stormcloaks have won, and they're the scapegoat. An invasion of Skyrim will be gruelling and if you win, you have the responsibility of rebuilding a now absolutley devasted province, as well as several more smaller rebellions on your hands. Now you're weakened with next war closer than ever. Let's say the Imperials win, you're still looking after a not-quite so devasted but still devasted province and still the chance for more rebellions, and the scapegoat is the Dominion. You can't just jump into a war with the Dominion to solidify your rule.
Fighting in Skyrim isn't impossible, and rebuilding the province would be the same as the Stormcloaks. Overseeing construction, dealing with bandits, enforcing laws. Keeping order etc. The Imperials aren't preparing an invasion force in Skyrim, and if push comes to shove they can and will conscript you. If war broke out between the Empire and Aldmeri Dominion the White-Gold Concordat is void, the Ban on Talos is lifted. So why would they continue to rebel? You Stormcloaks have the harder task, you're rebuilding, but also preparing to invade the Aldmeri Dominion and if war broke out right after, the Empire is in the best position, while you Stormcloaks either abandon Skyrim to fight or miss out on the war. Stormcloak victory would have rebellions pop up, small skirmishes between the remaining forces and whatever little recruitment they can do. Unless the Great War 2 broke out, then hostilities will drop.
Of course you can, the Legions are already in position. The longer you wait, the more rebellions spring up, the more damage the Thalmor can cause.
And I see where he's coming from and it's completely justified. It's a still a Legionaire with disdain for Nords.
And? I'm sure there are countless ex Legionaries who hate High Elves and Bosmer. War and conflict does that to people, it isn't a disdain out of spite. But one that grows from first hand experience, unable to cope with the horrors. There could be some who simply hate others for the sake of it, but what can you do? You get that in our world. Tamriel isn't perfect, but the Empire worked together for the most part. So even if a few disliked each other, the majority were fine.
I could throw up a Nord in Oblivion who fled Skyrim to avoid service in the Legions. Use him as the example average. Wouldn't be fair to judge an entire society over one example.
They still had the Elder Council with same power the Mede's had and they never had the substantial problems with the Legions the Mede's have and they never had provinces breaking off left and right.
That is like arguing the Reman Dynasty never had the same problems as the Akaviri leadership. Medes and Septims had different problems, and you can't compare them since they never faced the same tests. The Septim Dynasty never had a Great War, unless you count the War of the Red Diamond where High Rock and Skyrim rebelled against the Empire and an Empress was killed, the Imperial City invaded and taken by the rebel forces.
What do you mean provinces breaking off left and right? Morrowind, Elsweyr and Black Marsh were lost under Ocato. Summerset Isle was lost since it was simply too far to maintain influence and authority due to the Stormcrown Interregnum. Valenwood was lost by a coup from the Thalmor and their allies, during the time the Empire was just trying to get stable under the Mede Dynasty. They were supporting the rebels for many years.
Hammerfell didn't want to leave the Empire, and was forced out to keep the peace. The only province trying to "break off" is Stormcloak half of Skyrim...