Windshear has been defined in my past experience as a sustained change in indicated airspeed of +/- 15kts, a change in rate of climb/decent of greater than 500 feet/min without a pitch change input from the pilot, an uncommanded change in pitch attitude of +/- 5 degrees.
You are quite correct in stating that pilot reports of +/- 5 kts all the way down final as a windshear report is incorrect. especially if any of the reported conditions are not sustained as would be the case in gusty conditions. The intentions are almost always well meaning. It might be argued that a smaller aircraft might report windshear when conditions are less severe than those that I have listed, after all a report of turbulence of any intensity must be considered in the context of the aircraft type that reports it.