This is only good for Micron if 4F^2 is actually unachievable though.

If others end up making denser cells and Micron can't they will genuinely be behind. 6/4=1.5. It is not a small improvement.

I think this is definitely the "interest rates are high, dropping research and just pushing out what we already makes gives us a higher valuation" type thing which can kill companies.

This describes Intel perfectly circa 2010

Every tech giant that fell behind was once regarded as very technologically adept. DEC, Intel, SGI, many of them.