I am not surprised - when I ran tests in Rhino 6, its native render was faster and produced higher quality images than Flamingo. Flamingo has always been mediocre renderer, but it made good trees, shrubs, weeds, and other ground cover. The only flaw of the Flamingo plant editor is that it cannot make dense grass. I use these plants in Rhino 7 and I would like to use them in Rhino 8. For several years I advocated separating the Flamingo plant editor from the Flamingo renderer and integrating the plant editor with Rhino (like Grasshopper). I still believe that it is good idea. It seems that Roy Hirshkowitz (the maker of Flamingo) avoids debate about the future of Flamingo.
A new plugin called Rhino Nature also makes good trees, shrubs, weeds, grass, and other ground cover, but it is still in beta testing. Technical debate about the Rhino Nature plugin is here: Rhino Nature Plugin - Alpha stage is completed
Future Rhino Nature website is here: http://rhinonature.com/