You are overthinking this. If you like green tea, but an instance admin prefers coffee, would you stop posting on every community on that instance? Do you only want to post where people 100% align with your views on everything? I guess not, because then you would have to host a private instance where you only talk to yourself. Therefore, stop overthinking this and keep posting there.
If the question whether somebody federates with Threads or not is THAT important to you, then you already have your answer.
Overall, I really hope we do not come to a point where thoughts like “my instance does not federate with $evilinstance, therefore it’s a good instance. But $otherinstance does, therefore $otherinstance sucks and I’ll avoid everything on $otherinstance” become the norm. Because then we get a clusterfuck.