Hi @RyanChallender
I am not sure about this question. I suspect that the answer they are looking for is that projections seek to preserve some properties from distortions (although they can't preserve them all).
However, I don't think it's accurate to say that a GCS distorts properties. I think what they probably mean is that if you draw a map with a GCS, then properties will be distorted. Technically, you can't draw a map with a GCS, because it is impossible to draw the round earth on a flat surface without a projection. So when you tell ArcGIS to make a flat map with a GCS, it is forced to choose a projection (otherwise it wouldn't be able to display your data at all). It draws using a pseudo Plate Carrée projection. This is just latitude and longitude represented as a simple grid of squares. It is called pseudo because it is measured in angular units (degrees) rather than linear units (meters). This projection is easy to understand and easy to compute, but it also distorts all areas, angles, and distances.
So yes - if you choose a GCS for your map, everything will be distorted. However, it's not the GCS that is doing the distorting, it's the pseudo plate caree projection that is used behind the scenes.
I explain all of this better in this article: https://www.esri.com/arcgis-blog/products/arcgis-pro/mapping/gcs_vs_pcs/ Hopefully it can make this clearer.
