LL
No no, he's... got a point.
I would be dishonest if I didn't admit that 90% of my post was to mock an incompetent user, but there is a small nugget of truth to my words. Grand Admiral Thrawn micromanaged his campaign against the New Republic and was present during the major engagements; he will be the primary target during military conflicts and he was assassinated by a well-placed bodyguard.
I'm not sure if this would happen here, since there's a "no betrayal" rule (WTF), but I guess you can circumvent that by saying Thrawn's potential assassin would be loyal to the Galactic Alliance the entire time....
Anywho, joking aside, Thrawn isn't some walking deus ex machina who is capable of shifting the tide of a war unless he is properly equipped. Zahn lampshaded this in the Hand of Thrawn trilogy where members of the New Republic Senate successfully rebutted the fears of their more paranoid members; Thrawn increased the size of the Empire during his command but he wasn't a stone's throw away from topping the New Republic (he was beating them, but it's not like he was a moment's away from absolute success) and the Galactic Alliance is likely more militarized and organized than the fledgling New Republic and carries moar capable strategists.
That said, the Remnant would definitely join Thrawn, enhancing his forces dramatically. The Jedi would probably not, since they refused to join the Confederation, and Thrawn would likely turn his attention to them if he succeeded. It would be close, but Thrawn could pull it off.
But I can also see him losing this one, too.