That is completely wrong.

For foveated rendering one could easily build dedicate hardware into the device which would require almost no additional power. And those algorithms are not that expensive to begin with. Every camera has face tracking build in (which basically is the same problem) and that does not drain the battery either.

And why should northern Europeans eyes work differently?

Even if that would be true one could add a bunch of settings for personalisation.

Eye distance for example is a common setting on dodays devices...