Kemal was certainly a very capable military leader, but it is as a political leader that he becomes "exceptional". Another officer might have risen to lead the Turkish nationalist opposition against Sevres, but Kemal did many things that another general might not do.
During the Turkish War of Independence, would another, like Kazim Karabekir, have openly defied the Sultan, or be even able to hold the rather disparate Turkish national movement together? Kemal's charisma, perseverance and nerve even in the face of defeat were an important factor in the final victory.
And assuming that the war did go as IOTL, questions like the abolition of the Caliphate, the language and alphabet reforms or the one-party state would certainly be dealt with differently by anyone else. Kemal was probably exceptionally western-oriented, even among his peers. Under another, the general thrust towards modernization and Westernization would have remained, but the tempo would most likely have been slower and more gradual. Ironically, this would probably be all more the case if the alt-Ataturk allowed a real, multi-party system. On the other hand, Kemal ran the country not as a general, but as a politician (albeit an authoritarian one). Someone else might have opted for an even more pronounced army role, or an outright military dictatorship a la Franco, or perhaps become another Reza Shah.