Linken's is less about blocking spirit damage and more about keeping yourself safe from unit-target effects/control, such as M&K ult or Curse.
I think it would be an excellent addition.
Honestly a pretty pointless and bad change to knockdown, it currently serves as a safe and reliable interrupt item to counter flying heroes (among other uses). What good would come from hyper-nerfing it to be a niche point-blank airborne melee item? How are you going to melee a Vindicta?
