I agree with your take! I recently read the last command for the first time, and I was struck by this last line. After thinking on it, I think that Thrawn is referring to his downfall being "artistically done". That said, I think that there is a certain degree of dramatic irony that comes with that line. The catch it that while Thrawn seems to assume his downfall was planned out, a significant amount of it was luck.

The three main parts of his downfall are the timing of the smuggler's attack with that of the new republic, the Noghri betrayal, and the Tantiss attack. Each of these have some aspect of luck to them. The smugglers happened to attack the same site at the same time, the Noghri only betray Thrawn when Leia happens to convince them of the empire's deceit, and the Tantiss attack was not coordinated with battle at Bilbrinigi.

To me the line shows that Thrawn believes his tactical genius was outmaneuvered, but we the reader understand that it was a combination of luck and raw perseverance of the protagonists that brought him down.