I expect this effect is not ignored. But please note that heavy stars do not burn in billions of years but in millions. Not seeing them locally suggests that we

I expect this effect is not ignored. But please note that heavy stars do not burn in billions of years but in millions. Not seeing them locally suggests that we have slower starformation, not that we had more of them (heavy stars) billions of years ago. https://en.wikipedia.org/wiki/Stellar_evolution https://en.wikipedia.org/wiki/Stellar_evolution