We infer from the evidence we have that it is the Echo that prevents people from being tempered by Primals. But Fordola and Zenos have a manufactured Echo. However the evidence shows that this prevents Fordola from being tempered too. Nothing about any of those three statements demonstrates that the WoL hasn't been tempered so I'm confused how you are inferring that.
I'm not sure where the concept that Hydaelyn represents free will comes from. Hydaelyn represents a last ditch, desperate attempt by the 14th and (possibly) others to stop the rest of their people from sacrificing the new life Zodiark created. Her existence is predicated on opposing Zodiark and his followers. That's it. She certainly didn't offer Minfilia a choice when she had Minfilia run back into range of Y'shtola's Flow spell. It may be that Minfilia would have agreed, but she was never offered the option.
I have no idea whether the WoL has been tempered or not, I am just genuinely confused by the ardor with which people embrace the idea they haven't. Just as they embrace the idea that Zodiark is bad, Hydaelyn good. Personally I am waiting until I have something definitive to base my conclusions on.