the idea that Tim Duncan's is an 'underrated player' is remarkably overdone
And my point to you is that Duncan is not "underrated" or "overrated" at all. He's widely believed to be the greatest PF ever... one of the top 10 players of all time... He's properly rated as such.
Sure. You quoted Simmons's ranking of Duncan as part of your case -- go dust it off and read the whole section on Duncan: the whole thing is about how underrated he is. There was also that whole Duncan/South Park column, and beyond the ESPNers you can't find a single Yahoo et. al article about the Spurs that doesn't at least allude to Duncan's tireless consistency and underappreciated demeanor, etc.
I think there is a massive disconnect with respect to Tim Duncan and the Spurs, though maybe that has changed as a result of these last two high-profile Finals.
Every dedicated and passionate basketball fan has known for at least a decade that Tim Duncan is one of the greatest to ever play the game. But not all basketball fans are so dedicated and passionate; to casual fans, Tim Duncan (and the Spurs in general) have never been exciting enough to capture their attention. If you ask a random person off the street who the best power forward of all time is, you probably won't hear Tim Duncan's name. But if you ask any basketball nerd or reporter or anything, Tim Duncan will be the first name mentioned.
So, there is a segment of the population for which he is underrated in comparison to players like Kobe or LeBron who are more marketable and famous outside of us obsessive fans.