It’s a bit more complicated than this, since in his treatment of “neo-Darwinian theory”, Sanford makes a host of extremely dubious assumptions about the DFE of mutations. He arrives only at his conclusion by assuming the near-constancy of an extremely deleterious-skewed distribution, which has never been verified by measurement in any experimental or wild population of organisms.
So the conclusion here should be stated more like this:
Rather, his thesis is that given only his personally imagined constant DFE of mutation/selection (given only neo-Darwinian theory plus Sanford’s very idiosyncratic, empirically unverified and constant DFE of mutations), all species must go extinct. The corollary being that if life on earth is old, then Sanford’s personal, synthetic caricature of neo-Darwinian theory is false.