The French were pulling out regardless. Constantine's return merely gave them a good excuse. They were already negotiating with Ataturk. Why would the people of Greece, who were very anti-war in general by this point, unite under Venizelos simply because the king didn't interfere with his plans for Megali Idea? It wasn't a universal ideal in Greece.
While it's true that the French - and British - had other things on their mind than just who was king in Greece when they were formulating their Turkish policy, it was still a very relevant concern. The Anglo-French antagonism with Greece that mounted between late 1920 and 1922 probably wouldn't have been nearly so bad with Venizelos and Alexandros still at the helm. And the war
was a very close-run thing; the Republic's army was fairly small and its ammunition and logistics situation was pretty much just as bad as that of the Greek army during the Sakarya campaign.
It's not as though the Greeks and Turks proposed and the French and British disposed; Atatürk and his followers might reasonably have expected to pull out some kind of victory even if France hadn't switched sides, and Konstantinos and Papoulas had a shot at victory even though France
did. Imagining the Greek army running a slightly different - probably less aggressive - campaign in 1921, and without the Turks receiving the benefit of France's volte-face...well, they probably had a better shot than they would've otherwise. Maybe. Either way, it would've been close.
Venizelos might have had better relations with the Allies (although from what I understand of Versailles the Big Three mostly thought he was annoying), but it's really important to note just how uneven his support at home was. He won elections and plebiscites frequently, but also lost them - and tried to contravene the decisions implicit in these often enough that labeling him as 'democratic' and the likes of Konstantinos as 'monarchist' is painfully inaccurate. His backing in the army was similarly uneven; he had embarrassingly few supporters in uniform in 1916-17, meaning his breakaway Thessalonikan state rested on
Allied bayonets, not Greek ones. He had more supporters there in 1920, but not enough to make up for the popularity of Konstantinos as an alternative option. What that usually meant on the ground is that he had just as many die-hard enemies as die-hard backers. And that meant a legacy of divisiveness for which he and his policies are at least partly at fault.
I think that he is a big beneficiary of nostalgia among Greeks, especially for the Great Idea, and that he gets an undue amount of credit for his republicanism and for his political enemies' spectacular failures while rarely being held accountable for his
own spectacular failures.
My own favorite Greek is probably Seleukos I but that is neither here nor there
