The common-knowledge number seems to be about 70% of open source projects are under the GPL and (more importantly) many of the most crucial and successful ones are.

I am calling bullshit on that number. The vast majority of libraries in modern languages are under far more permissive licences, MIT, Apache2, etc. So most libraries for python in pip, rust in crate.io, node in npm, golang modules etc Which makes up a huge amount of software projects. These are languages and libraries used by companies for their own closed source products or tooling for these langauges and a huge amount of success for these is due to their permissive licenses. Companies would not touch GPLed libraries in the same way which would drastically reduce the amount these sources are used and thus their overall contents.

If you only look at the linux desktop you might see more GPLed software, but that is not the majority of opensource software. I don’t know the real percentages of everything, but 70% is a made up number. I would not be surprised if it was 70% being under a permissive license.