We may have different definitions of walking distance from downtown because I think that both Volunteer and Washington Park fall in that range, although I understand that they are farther than a hypothetical South Lake Union park. On the other hand, I would note that neither Golden Gate Park nor Central Park are near their respective downtowns.
I don't really disagree, but it's a 50 minute (uphill) walk from Pike Place to Volunteer Park, whereas it's 15 minutes to the edge of SLU. I don't really mind walking an hour, but many people do.
Golden Gate is a little out of the way, Central Park is super accessible by subway.