please refer to MOF website
Ministry Of Finance - Our Policies

it says
"The SRS offers attractive tax benefits. Contributions to SRS are eligible for tax relief, investment returns are accumulated tax-free and only 50% of the withdrawals from SRS are taxable at retirement (referred to as a “50% tax concession”).
"

i emailed MOF, they refer me to IRAS
and IRAS did not reply my query "Is SRS capital gains tax-free" directly

so, my conclusion is the same as yours, a good investors will pay more tax thru SRS
then again, in the later years, you can manage the contributions and withdrawal to derive max benefits (or lowest tax)

and of course, its unlikely to get consistently good ROI for 30yrs.
for me, after 6yrs, my SRS balance = my contributions
last few years were tough