As long as the government value the finance industry more than engineering, finance grads will always earn more on the whole, regardless of whether they are bright sparks or average performer. We're talking about what's the best industry to go into for the average student. If you're a bright spark, no matter where you go you'll still do well (with a bit of luck of course).
I give you 2 extreme examples to illustrate my point:
Imagine you're average, and you decide to do ballet. How to survive in Singapore as an average ballerina?
Now imagine you're an average back office operations guy in UOB bank or MAS. You'll have a stable career with above-average pay barring unforeseen circumstances like retrenchments (UOB has no retrenchment thus far in this crisis and MAS has never retrenched any staff).