Do you even know where Strathfield is?
Strathfield is the outer most boundary of inner west, 15.6km from Strathfield to SYD vs 48.9km to WSI. So WSI is 3 times the distance away, so no way will it cost the same in a uber to get to both airports from there.
Paramatta is also 10km closer to SYD than WSI, so whilst the fare difference will be less it should still be more to WSI.
South West Sydney (Liverpool, Campbeltown) will be closer to WSI, but if already on the airport line which Campbeltown is could still be quicker to take the direct train to SYD rather than multiple changes to get to WSI.
Any small savings for flying from WSI over SYD for anyone living in the East, North, Inner West or Inner South would be more than offset by the extra transport costs to get to WSI.
If you live in the South West or outer Western burbs then WSI will be cheaper if there is actually a flight from there to where you want to go.