Scenario One: Thanos is given a hundred and one years of prep to study and figuring out how to take down Odin, deal with the Odin force, Thor, and the Loki and the rest of Asgard all the while seeing about trying to also take the Odin force for himself. This is the version of Odin that beat down Thanos.
Scenario two: Thanos switches places with the version of Odin that beat him down, they switch resources, Thanos has the odin force, all of odins resources and rules over asgard as he did-- he has to deal with Loki and everyone else Odin did. Odin gets all of the resources Thanos had (And all his knowledge being one of them) his own son Thor.