But it is still lesser than the tax I would have to pay when I have income right? Assuming your SRS has been earning 0% return....
OK, in your first scenario you withdraw $40,000, have no other income, and you pay $2,550 in tax. (That figure is the maximum, with no other income. You still might qualify for a modest amount of tax relief, probably.)
I'm going to modify your second scenario a bit. In my alternative scenario you withdraw $40,000 after reaching age 62, you have other taxable income -- let's suppose $80,000 -- and thus you pay 11.5% tax on half the $40K = $2,300.
So that doesn't work. You need to have rather high income in your age 62+ years to make the math you describe work. But it's mathematically possible.
What you're fundamentally asking is whether you can/should use SRS as a vehicle to defer taxable income into an otherwise non-taxable calendar year, with the assumption that you're probably going to receive taxable income (such as significant rental income) in your retirement years. And the answer to that question is, "Yes, that often makes sense." You still want to try to achieve some reasonable returns on that money, even if you park the money in Singapore Government Securities (which you can do), but yes, that can make sense. The fundamental reason is that the government doesn't appear to charge the marginal tax rate from when you made the contribution(s) if you withdraw the funds early. (Free tip to IRAS: that'd be an effective way to close this particular loophole, if you view it as a loophole.)
Most people can neither predict nor aspire to earn zero (or near zero) income, so using SRS to defer income in the way you describe is not something that's easy to pull off successfully. But if you do have such visibility and inclinations, I say "Go for it."