American IQ scores have rapidly dropped, proving the 'Reverse Flynn effect'

Intelligence can't be generalised.

You could put the most intelligent person in the Savanna and they would just die, whilst a bushman will survive. Who was smarter in the end?

hmmm, but if you have two bushmen, one with a high IQ and one with a low IQ who will better survive. Or what if the most intelligent person in the Savanna was a bushman...So it depends on what you consider intelligence. Critical thinking is part of IQ testing and I would expect a wiley bushman to be good at critical thinking if he is going to survive.

the most intelligent person, you already answered your question

most intelligent according to your IQ metrics

Exactly. People that want to apply IQ see it as a general performance metric. But general performance has many different aspects. In the example of the bushman it does not matter how fast you can count the alphabet,.it won't be helping your survival.