Is IQ a good measure of intelligence? If so, and if intelligence is inate, why is the Flynn Effect a thing?

If we get better at teaching a topic to people, such that it is more accurately and efficiently encoded, and they can therefore utilise that information more readily, they will engage with related information more intelligently. The reason they do so is how the information was presented to them, not anything inate to them. In addition, if intelligence is inate, why are all of the world's high-performing people where they are due to hours spent in purposeful and directed practice (often under someone's tutelage) rather than any antecedent ability?

Finally, which intelligence? Fluid or crystallized?