Chatting with a Singaporean a while ago, we touched the taxation system in Germany. And, I have to admit that I may not know exactly how it works nowadays, because I have been out of Germany for many years. However, from what I remember about my motherland, I can easily conclude that nothing changes very fast. And the changes are not always for the better for the people. They are often designed for political window-dressing as a result of some half-hearted promises given before election.
Why Not Making it Simple?

Conclusion
In my opinion, IRAS is one of the showcase institutions for continuous improvement and innovation to the benefit of tax payers in Singapore. And, highly effective processes are usually efficient, too. I.e., management and staff have been optimising their internal processes to be able to support the well-known excellent service delivery with minimal effort.