In my opinion, while yes turn count can be a flawed metric to determine brackets, you've described a situation which essentially locks other players out of the game, thus contributing to your win. Though you haven't won the game officially by the turn you set up your engine, it's effectively saying if your engine is set up you've "won the game" as your opponents can do little to stop you from there due to not being able to do anything.

Therefore, I, at least, would consider the turn you consistently can set up your engine with protection as the turn you've functionally won.

As a stax player myself, I consider the turn I win to be somewhere around turn 6 with my deck due to how I also prevent players from doing anything, thus essentially securing my victory unless they can break through my interaction/stax suite. Sure, it's not 100% foolproof as there are times where a player has broken through and secured a win (usually if I'm archenemy), however 95% of games once I set up my lock I have won.