Putin has invested significant resources into owning Ukraine, too, so if people have a right to own whatever they invest significant resources into, then Putin has a right to own Ukraine.
Yes, but (continuing the argument) the rest of the world has also invested significant resources into Ukraine to counter his ownership claim (in a way that never really happened while he was solidifying his hold on Russia).
It was when he wanted to own Ukraine that it rose to the level of significant intervention by the outside world.