You do realize that your routing cleverly avoids all the routes that offer the higher-quality F service and you only have 2 real F sectors (LHR-EZE and HKG-JNB). DONE5 would be almost the same travel experience as AONE5 as most of your flights either don't have F or have a stripped down F (CAI-LHR, SYD-NRT).
The lower country prices are typically only for travel originating there, and not for SOTO or SOTI. I doubt that you can use that cheaper MRU fare for travel LHR-MRU (but I haven't checked the fare).