Both scenarios would cause upheaval, and I'm not sure what he means by a "rich state of equilibrium".
“Rich” refers to the variety and abundance of living things. The total biomass of living things has declined (there’s less overall) and what is left is concentrated into far fewer species than previously.
Just taken as a store of information, the loss is staggering. But from a practical perspective we are less rich; it’s far harder today to catch fish than it used to be, for example.
I know some biologists, and they often wish that the world should be "rich" from a biologist's perspective even if the biologist isn't there to observe it.
It's a curious perspective to me. If you don't exist, why would it matter whether the world is (a) green and buzzing with insects, or (b) reduced to grey goo or strange matter? Why would your aesthetic preferences be relevant in a world that you don't exist in? It's not like you're going to get to watch this universe through a viewport.
It's not about "biology". It's about roles in the ecosystem.
A direct question would be easy to answer. As it is, I'm sorry to hear about your confusion :-)
An aesthetic preference is essentially an ideal against which we compare our experience. Whether we expect to meet that ideal does not diminish its power. In fact if it was easily met, it would not be much of an ideal.
[0] https://cosmosmagazine.com/earth/sustainability/chernobyl-is...
An icy comet circling way out beyond Neptune is an example of a system somewhat near equilibrium.