Not a very good comparison I'm afraid, Sears didn't lose to an other company who was offering the same service, they lost to a series of companies that offered the same utility but in a very different way.
DDG is mostly just offering the same service as Google (really, only a fraction of the service because Google is a lot more than Search these days). As such I expect that at this point if a Google-killer appears it's also be a DDG killer as collateral damage.
is he making that comparison? i read it as, ddg may not bring down google, but something eventually will, which seems exactly what you are saying too...
DDG is mostly just offering the same service as Google (really, only a fraction of the service because Google is a lot more than Search these days). As such I expect that at this point if a Google-killer appears it's also be a DDG killer as collateral damage.