As a nearsighted human who didn't get glasses as early as he should have, I used to use people's gait or clothing to recognize them at long distances. You know your dog best, just saying there can be ways to compensate.
Without a doubt, yes, all sorts of compensation are at play. Still, the fact remains that he reliably picks up my relatively subdued sign language at great distance. And swimming, even in rough sea, if he can't pick out the floating stick, he'll look to me, I'll point, he will scan as directed, and head straight for the thing. One way or the other, all this is decent visual performance, nothing nearsighted about it.