(a) windshear relates to inflight handling and performance .. we are concerned about AIRspeed. The problems generally are transient (ie short-lived) ... and are related to the mass of the aircraft ... bigger aircraft ... greater mass (inertia) .. takes longer for the aircraft to shake its head and adjust to the changing wind field.
(b) navigation relates to speed referenced to the ground ... we are concerned about GROUNDspeed
I think you are focussing on groundspeed .. which results in understandable confusion ?