Assuming that he books SYD-LHR rather than booking it as SYD-BKK/SIN-LHR , he will earn
On AA: the base of 10,586 plus 10% Cabin bonus of 1059 plus Platinum bonus of 10,586 giving 22,231 . r/t gives 44,462. He will also earn either 250 or 1000 each way between LHR and AMS depending on the fare basis giving a total of either 44,962 or 46,462
If he books it as SYD-SIN-LHR, then he would only get the platinum bonus from the SIN-LHR sector so would reduce the overall earn by about 3908
On QF, his earning would be 10,586 plus cabin bonus of 25% of 2647 on the SYD-LHR run giving 13233 . r/t gives 26,466. He would also earn 125 or 500 each way on the flights between LHR and AMS giving a total of 26,966 or 27,466
As far as QF status goes, if he does SYD-LHR-AMS r/t , he would earn 240 SCs and as SYD-SIN/BKK-LHR-AMS r/t , 300SCs so wouldn't actually even make silver status
Would seem to be a no brainer to take the candy to me
Dave