Yes, Crimea does indeed de facto belong to Russia, although de jure it is recognised by most countries as belonging to Ukraine.
Again, I assert that I am mayor of Moscow.
The difference between your assertion and this situation Is that in addition to asserting that Crimea is now a part of Russia they also control and govern it. I don’t think there is a lot anyone can do about that.
I don’t think that’s a contentious claim to make, it’s simply just the reality of it.
What will be more interesting will be to see how far Western/NATO countries will go to change that reality and how far Russia will go to prevent that.