Even after years of this discussion - none of the esteemed, resourceful people on this board have provided a single reference to a fund, investor, charity, trust, public investment committee, school PTA or even a financial blogger on YouTube that states they will only make an equity investment in companies that have their debt rated investment grade by two or more CRAs - despite many, many, thousands of said groups publishing their investment criteria on their websites in plain english.
This is the same group that investigated the metallurgy of gigacastings, the benefits and drawbacks of different magnetic field configurations of various electric motors, the raw material export policies of foreign nations that don't publish in English, and arcane tax documentation covering hundreds of thousands of pages.
The investment criteria people are assuming above does not exist - at best there could be a correlation because the factors that cause CRAs to rate company debt investment grade are similar to the criteria that conservative investors are interested in.
It would take a few minutes of googling to prove me wrong with a relevant document from a fund - but I doubt anyone will find an example.