Very interesting, but...the prevalence of G2 stars would have required heavy element burning in at least one or two earlier generations of larger stars, which would have required at least a few billion years including supernova production, element spreading and subsequent accretion. I’m a little fuzzy about how this then young galaxy could produce so many G2s.
Bureaucracy.........
Not for big stars. A 10 solar mass star might burn brightly for only 100,000,000 years or less and then go supernova. Voila! lots of metals available in a short time.