I think the parent's point was providing evidence that the lack of biodiversity causes harm. To put this plainly - if every banana that is harvested in a farm and consumed by a human is identical, then so what? It doesn't mean bananas that aren't harvested by humans also will share that same DNA.

Even then, if every banana in the world was genetically identical what harmful effect would this have? I can probably speculate, but I'm genuinely curious what the science says.