I'm not sure what you are trying to argue here. Just because he didn't need every vry'kul to die obviously means they didn't want to die for him though.We don't know how many of the Vrykul back then have free will (and by that, I assume you meant being born naturally instead of being created, since they were still being created artificially during the Ordering of Azeroth). I'm pretty sure he didn't need half of the Vrykul to become Val'kyr, though. Chronicle only stated that Helya argued that Odyn shouldn't enslave the Vrykul with free-will to obey him (this applies only to the Val'kyr, not the Valarjar). However, her argument - while morally makes sense - might not be correct. Having free will doesn't change the fact that they were created to assist the Keepers in their Azeroth-related tasks.
pretty sure their mantel of responsibility died when the Dragons were elevated weren't it? And it still comes back to the fact that his own pride made him kill Heyla, and his picture of his own fairy tale valor land.Odyn breaking himself of the other Keepers didn't stop him from being a Keeper, the Prime Designate or protecting Azeroth. She was still obligated to listen to him as he still had all the requirements.