But that is quite ahistorical.
The borders in Europe have been subject to constant change. There is no sovereign authority with either the power or the right to fix them at a given point in time, to stand "forever".
That the borders of today will resemble the borders in 50 years is quite unlikely.
Not "constant". Change, yes; but each change was nevertheless evaluated as for its justice or injustice. This change that Putin forced is not legal. The change of the Maidan, however, is legal.
The history of Europe is indeed long, but so is the history of cooperation between sovereign states. This is why we had the Peace of Westphalia, for example. Europe is not a jungle the putinista try to drag it into. The EU is expressly put together to provide a legal framework for cooperation and stabilize the borders. There is nothing wrong with that.