There’s a big difference between the default route fare for this journey and the several alternative routes. I’m assuming that as all the latter involve changing from Nat Rail to underground the default route must mean avoiding the tube, but the exact route is not specified. So I’m guessing Crystal Palace to London Bridge on Southern (or CP to New Cross Gate on Overground and change for Southern to LBr), then Thameslink from LBr to STP. What do you reckon?
Yes, the default route is anything that doesn’t involve changing between stations for the Underground. You could change at Whitechapel and Farringdon as they can’t tell you’ve done that instead of via London Bridge.