This edit was added after my initial reply:

>...but ultimately there is no universal way to come up with one definitive ranking, so we will debate it forever.

WAR is a universal way to come up with a definitive ranking. It's a framework for measuring player contributions that is applied equally to all players. That's not to say it is the universal way, but the beauty of WAR is that the framework can be re-created to value or devalue player contributions as one sees fit and then use those criteria to measure all player contributions.

That's why the authors of this paper cite the two most common WAR frameworks (bWAR and fWAR). And it's why they've created their own version which incorporates a measure of the available talent pool at the time of each player's career.