Haven't grown up in a 3rd world country - I disagree with you.
Most countries in SG's state at that time never made it past these initial stages of growth.
Why? You can still start from zero and remain there.
Because there's lots of low hanging fruit in terms of infrastructure, education, technology, etc. You don't really need to innovate, you can just copy other successful countries.
if it's so easy we would see more 3rd world countries advancing past their current state.
At the time of independence, people were very pessimistic about Singapore's prospects, it just looks inevitable now given their rise.
Corruption, incompetence, war, geographic disadvantage, etc.
Tell that to like almost all the countries in the world.
Many countries in the world are growing at a fast pace right now - there's less poverty that there was ever been.