LKY and the current generation of political leaders also believe that China will have a larger military footprint than the US in the Singapore Straits in the future.
So should Singapore ditch the USA in such a scenario?
Nobody is ditching anyone.
ASEAN is desperate for the US to remain involved in the Asia-Pacific in order to balance China's overwhelming power.
If the US is not enough, don't be surprised when in the future they start courting EU/India.
That's how International Relations work in geopolitics. The moment someone gets too powerful, you start inviting outside parties to balance him out. Why else do you think that ASEAN loves involving the US in the SCS dispute