Thrawn is NOT a great strategist
Operational Artist, not a Strategist.
Okay, before you all come at me with torches and pitchforks, let me say that I love Thrawn in both Legends and canon. However, while he has demonstrated truly amazing tactical and operational skill—arguably at a genius level—I don't think he's actually a great strategist.
First, let's distinguish between tactics, operations, and strategy.
Tactics is how you win the immediate fight. Here, Thrawn is pretty dang close to perfect. He wins just about every fleet engagement he's involved in, often against considerable disadvantages. No argument from me: the man is a tactical genius.
Operations is how you connect individual battles and other military actions so that they achieve a larger military objective. This is where things like logistics, tempo, concentration of force, maneuver, reserves, intelligence, and deception come into play. Once again, Thrawn is brilliant. His campaign against the New Republic demonstrates an extraordinary ability to make limited Imperial resources achieve disproportionate results. He consistently creates situations in which the New Republic has to react to him rather than the other way around.
Strategy, however, is about using military power to accomplish political objectives.
And this is where I have questions.
By the end of the Thrawn Trilogy, I still don't see a convincing path from "Thrawn keeps winning battles" to "the New Republic is destroyed."
Let's assume Thrawn isn't killed by Rukh at Bilbringi. Let's go even further and assume that he wins the battle. What happens next?
The New Republic has started figuring him out. He's lost Joruus C'baoth and therefore his Force-assisted coordination advantage. He's lost Delta Source. Admiral Ackbar is back in command, and the political divisions Thrawn exploited are beginning to heal. The New Republic now knows exactly what kind of threat it's facing.
Yes, more Imperial warlords might start joining Thrawn after further victories. But that creates another problem: Thrawn can't be everywhere, and let's be honest, most of the Imperial warlords can't be trusted any farther than C-3PO can throw them. Giving Thrawn more ships commanded by unreliable, ambitious subordinates doesn't necessarily solve his fundamental problem.
And that's the part of his strategy that I don't understand.
What is Thrawn's actual theory of victory?
Winning more battles isn't a theory of victory by itself. Taking more systems isn't necessarily one either. How does Thrawn turn those victories into the collapse of the New Republic as a political entity? Does he intend to capture Coruscant? Force the Republic to negotiate? Trigger enough political fragmentation that member worlds secede? Destroy the New Republic military until the government becomes indefensible? Reconstitute enough of the Empire that worlds begin defecting voluntarily?
Maybe there is an answer, but I don't think the Thrawn Trilogy ever gives us a particularly convincing one.
So my argument isn't that Thrawn is overrated as a military commander. Quite the opposite. I think he's one of the best tactical and operational commanders in Star Wars.
I'm just not convinced he's a great strategist.
He knows how to win battles. He knows how to run a campaign.
I'm not sure he ever demonstrates how those victories are supposed to win the war.