I'm damn good myself(not gpa) but I got rejected from all 3 uni. Seriously.
Not sure about nus/ntu, I went to smu for SIS interview they have the students project posters pasted all over the wall. While waiting for my turn, I did read in detail what most of the project does and the programming language and api they used, it was definitely doable by myself. An example a web application using php and google map api, I could do that!
Anyway,
After the 1st SMU ISM interview, I was informed about a coding challenge to see my aptitude for programming, So I unlocked the challenge and went down to the "live" coding challenge. There were only 3 of us, 2 guys 1 girl.
The challenge was actually same as what we were required to do "online" with maybe slight modifications (or same questions) anway it was basic programming stuff, looping, functions etc.
1st guy - He did the coding super fast, he finished 10 questions in 7 mins. He is either really talented+careful or a JC student, memorize all the questions
Anyway I was really amazed and good job to him.
Me - I didn't bother practising because to me those are doable , it is in my blood. So I finish 10 questions in 30-40mins. Reason I took so long is because I was careless (forget to reset a counter) however I answer all questions correctly and on time.
Girl - I think she only managed 5 out of 10 questions by the end of the 45mins given.
In the interview after we finished our challenge, the professor asked me what problems I had even though I finished all the coding correctly just that I took a longer time than the 1st guy. I told them I have no problems, just careless because I forgot to reset my counter...somehow they kept saying something like, "Ok so what took you so long, there must be some problems encountered" but really I was just careless, my algorithm was working fine just that I forget to freaking reset a variable...so no choice I have to anyhow bomb 1 problem and I stuttered because it was awkward to say something that didn't happen.
Anyway I must say that poly is not about play acting, talk more, participating.you really need to put effort into your studies/project to get good gpa. I even bring my programming projects back home to do. I myself is an introvert, I never ask my lecturer stuff as I have no need to / and on the occasion I don't know things, I'll just ask my friends or search around.
Sometimes I wonder If there are other stuff that a university can use to determine if a student is good but does not meet the entry criteria. SMU is trying to do that but it failed badly.
-Guy with gpa of 3.51