Controlling the Aegean with Turkey on Russia's side would be the problem, I suspect. It's not just the Black Sea Fleet you're facing, it's also air units ranging out of Turkish air bases, with the complete support of Turkey's own forces.
That's where formalities and reality collide.
Formally, Turkey is still in NATO and is its ally.
In reality, Turkey is going its own way and playing Russia and the rest of NATO against each other, picking the most convenient offer at the moment.
The S-400 choice was a long term commitment that to someone not familiar with military matters would seem like a piece of trade and technical trivia, but to someone who is, it made it clear that Turkey can no longer be counted as a reliable ally when it comes to a potential conflict with Russia - because a country that is one would not commit to using Russian designed, made and serviced strategic air defense system for several next decades, as that is not the kind of air defense system one wants to have if the main challenger for your air defense is the Russian air force.
So, whose air force is Turkey *really* worrying about if it's not the Russian one?
As such, can Turkey be trusted to side with NATO if it comes to a conflict with Russia?
With said technological dependence on Russia, can Turkey do that effectively at this point even if it wants to?
Or is it just going to leave NATO and declare neutrality the moment it happens, or worse, let Russian forces use its airspace and cross the Bosphorus at will?
Turkey is already on Russia's side, so the point is moot.
All we are doing by leaving the nukes in Turkey and allowing them to remain in NATO is hugging a viper to our chest. Better to end the charade on our terms, rather than allow Erdogan to continue this bullshit. Poland and the Baltic's are worthwhile allies, Turkey is most certainly not.
Turkey is the second largest army in NATO and holds a major strategic location, so i would not call it an unworthwhile ally. The question here is whether Turkey can still be considered an ally, formalities of being in NATO aside. Lately it's not acting like one in ways that go beyond talk and bluster...