I would argue that you have not exchanged like for like when you chose to be re-routed to GRU in F. I would rather sit in J on a direct flight (and spanking new 787!) than do the connection you have elected to accept on an old 772. Flying LHR to GIG (Rio) in F very nice. Flying LHR to GIG is J is also nice. Flying LHR to GRU (Sao Paulo) is very nice, but then hanging around in GRU for a connection to GIG (or SDU) on a LATAM single class service would completely eliminate all of the joie de vivre accumulated by the journey in the F cabin.