I'm seeing a very problematic difference between the size of objects in Google Earth vs the GoogleMAps layer of QuickMapServices (QMS). See the image, the footbridge over the Tyne comes out to 103 m wide in Google Earth but in the same image, QGIS gives it as 183 meters wide. I've had similar scaling isues when creating buffers based on polylines drawn from QMS base maps in QGIS. What I do there is create the vector in WGS84 UTM, digitise on the basemap, then buffer. But this gives sizes that are off by a similar factor to the scaling error in the image above.
What's going on?