He won the civil war, that's where he gets his legitimity. No terrorist attacks since 2015, and even then the terrorist group leaders said it wasn't on their orders. No transnational terrorism is also a good sign. The Kurds were very skeptical a year ago, and probably afraid too, but from the little I heard, they seem relieved about what is currently happening (Lebanese too, I don't have close friends in other related communities). I know the SDF would be a better winner overall, but you have to make with what you get.
Also the Kurd I know have family in the Hatay province and around idil, so he is _very_ confident that economically at least it will be a success.
And like I said elsewhere, you can see the Turkish/ottoman Sunni influence in his religion (in islam culture and religion are extremely close), which is a very good sign. And concerning the massacre: we mostly forgot about Smyrna, and even Dersim isn't cited when we talk about Atatürk (both at least one order of magnitude bigger). It is very sad, but at the time European powers wanted stability in the area, and Atatürk gave them that. I only wish for the war to end and to have the area stabilise, and unlike Iran or even Irak, I see a slight chance that that it might end correctly for the minorities (10%?). Which isn't much, but I would rather wait a year or two before casting judgment.