Actually closer to 3.4%.
I did a comparison using SQ Economy (using SQ flexi fares), Business and First/Suite fares. The business and first fares come out consistently to about 3.4 VM/$ (except for Taiwan as SQ has no First Class fares to Taipei). Economy fares went as high as 4% but I see those as less accurate since there can be quite a bit of seasonal fluctuation in Economy fares.
(BTW, using the 3.4% ratio, the 15,000 miles sign on bonus would be equivalent to $510, which is about what the annual fees are.)
So, if you look at it as a pure rebate card, that translates to air tickets rather than cash, this card isn't bad.
if you need 3.4VM to "pay" for every $1 of the ticket - this means that for local spend, you need to spend $3.40 to get OCBC to pay $1 of your ticket. This would mean an incredible 29.4% rebate.
could you recheck the math?
did you mean 34VM/$? in which case the rebate is 3%.