Here's the background of this policy of floating the SMRA rate. It was decided many, many years back and has already been delayed once. In fact, one assumption of the policy - that there is no 30-year SGS, so the government will just take the 10-year SGS yield and add 1% - is already quite out of date, because the government went ahead and issued a 30-year ordinary SGS in 2012.
So this policy, like all other elements of CPF, can be changed. Judging from recent policymaking trends and future needs, do you think the government is going to cut the SMRA rate? After adding this additional 1% interest for 55-year-olds, and pledging to increase their contribution rates further? So I predict this planned-but-never-implemented policy will also be revised. You can quote me on it.
There is always uncertainty about the future and about public policy. Contribution rates will change. Interest rates will change. Even the statutory minimum interest rate of 2.5% can be changed - you just change the law. It's not even the constitution (which can also be changed easily

). But we have to assume something for long term planning, so take the status quo policy.
But here's something interesting. Scenario: guy earns $2,200 per month
and never gets a raise. Works from age 25 to 55 - 30 years, so I assume a working life even shorter than the minister's 32 years. The applicable contribution rates are as follows:
Special Account (% of wage)
35 & below 6%
Above 35-45 7%
Above 45-50 8%
Above 50-55 10.5%
I also ignore the extra interest rate on total balances >$60k
and the new extra interest up to 6% for 55-year-olds and above. Let's apply a flat interest rate of 4% pa. His balance at age 55? About $108,600. At age 65, this balance would have grown to $160,700.
What if the SMRA rate is only 3% pa for all 30 working years? I am not even talking about current 10-year SGS yields + 1% = about 3.45%, I am taking the current 30-year SGS yield, 2.97%. His balance at age 55 will be $92,800. Age 65, $124,800.
We do not need gratuitous assumptions to show the broad conclusion - most people will have no problems meeting at least the Basic if not the Full Retirement Sum, so they have a healthy CPF LIFE payout. In fact, it takes gratuitous assumptions to prove the contrary. Don't be a sceptic, just work it out for yourself in Excel.