Do you agree that if a child is bright enough he or she can catch up and even outdo others later in primary school, and thus no need to invest in expensive private preschool? Or do you think it's better to build a strong foundation during preschool years so they won't lose out in primary school?

There is no need to place so much stress on the child. Let the child enjoy his childhood and teach him concepts through play. Build up his curiosity and let him ask as many questions as he wants. That way, he will be driven to learn by himself without the need for enrichment classes and expensive preschools.