Your business analysis is flawed. You might admit it to being non-business-like but I tell you, it's not even close.
Firstly, SQ will probably post a loss on the US routes, at your current analysis, SQ breaks even.
Secondly, insurance costs will hit hard.
Thirdly, since there will be fewer passengers, fares will be more heavily discounted.
Fourthly, you will lose more than 20% from Australia. Public opinion of SIA is not great, though not as bad as AirNZ.
Fifthly, implementation of their new IFE and new biz class will cost a lot of money, sure, one-off, but will cost money.
Need I go on?
M88, 722, 732, 733, 734, 73G, 73H, 742, 743, 744, 752, 762, 763, 772, 773, 77W, 320, 332, 333, 345, 388, DH8, SF3 - want