You may just be trying to disagree with the author for sport.
> we carry around only...
Not true. We can carry resistance to some ancestral pressure which isn't part of the current environment.
> sooner or later...
Yes, sooner when it's costly, later when it's less so, through normal evolutionary pressure (entropy and all).
The point is, most species at time T do carry traits that aren't that useful to them anymore. The costlier ones yield enough negative fitness points in evolutionary game theory to rid the gene pool of them quicker. It brings us right back to the author's original argument.