Have you read the following blog posts and their comments?

What’s not good about Supplementary Retirement Scheme (SRS) | Salary.sg - Your Salary in Singapore

Mr Wang Says So: The Supplementary Retirement Scheme

What I think is that in general, if you are a high earner you will benefit from SRS. But based on your analysis, it seems if a high earner who's also a very good investor may not benefit from the scheme.