You are right in what you wrote, but Turkey cannot withdraw it's forces from northern Syria after PKK is kicked out. Idlib pocket alone nearly has 3 million people, and Turkey is not hungry to get any more refugees. You should understand that. Hezbollah is not angel neither, if they get in Idlib there would be total massacre and millions of people will flee to Turkey.
Turkey wants to clean northern Syria with 30km-ish line and re-settle Syrians in Syria, and putting their military observation points (as per Astana Agreement with Russia-Iran) to ensure there won't be any more fighting.
But i would love to see some FSA/SAA common police forces to govern these regions, under Turkish observation. With this way, Syrian authority will represent in region so they will be happy, Turkey will be happy because no more PKK presence, and no more Syrian refugee convoys floading into them, Russia will be happy bcs they wont have to waste any more money into meaningles war, Iran will be happy bcs US will be kicked out of Syria.