There isn’t an unbiased metric in existance, not when intelligence is itself so ill-defined and nebulous.

You can’t reduce it down to a number or set of numbers without making judgements about what intelligence is and isn’t, or what the numbers represent specifically, or without making judgements about how to take the measurements. These judgements cannot be made but through the lens of the culture and individual life experience of judge(s). And when it comes to research on topics like this there is simply no way to truly isolate any measurable quantity out as being inherently caused by biology vs external factors. Humans are messy and hard to sort neatly.

If anything, the comic more-so reflects what happens to kids who grow up getting told they’re gifted and praised for being inherently smart rather than for working hard or other such things that they can actually exert any control over, thus producing kids who are terrified of not being as smart as they’re told they are or as “successful” as they’ve been expected to be, who grow up to fret about their failures or perceived failures. Or to kids who have or believe themselves a great deal of potential but cannot realize it for other reasons, be they economic, geopolitical, familial or whatever.