while the billionaire class is still a massive problem, an even larger problem ecologically is that tens of millions of moderately wealthy people from wealthy nations have massively outsized carbon footprints.

It is definitely false that that's a larger problem. The top corporations emit way more carbon than all the petite-bourgeois SUV drivers and so on. I think the number people constantly trot out is that the top 100 companies (a fraction of a fraction of a percent here) do 70% of the emitting.