Since basketball is the most statistically literate major sport, actually being "overrated" as an individual player is remarkably uncommon
Following Russell Westbrook's retirement, I witnessed polarizing opinions. Like when Kobe retired, there's a lot of post-retirement adulation, but the Westbrook loathers are having a ball. It is the most notable time for them to pridefully exclaim him as "overrated", and I realized that the idea of an "overrated" NBA player is often based more on extreme opinions than on the consensus view.
Russell Westbrook in specific had obvious athleticism and production, but his weaknesses are also very public, including turnovers, inefficient shooting, questionable decision-making and arguably stat-padding. Those flaws have been discussed for years, so describing Westbrook as overrated simply because some fans rate him too highly overlooks how the broader basketball community actually views him. The term overrated is overrated in that sense.
I mentioned Kobe earlier. Some of his most devoted supporters consider him the greatest player in NBA history, but that is far from the prevailing view. Michael Jordan has the stronger statistical and championship résumé, and a vast majority of basketball fans already recognize that. Using the most extreme Kobe supporters as evidence that Kobe himself is overrated confuses a small group of fans with the general perception of the player.
Underrated players are very different because unfamiliarity and general fame plays the primary role. For example, Sidney Moncrief was one of the best two-way guards of his era, won Defensive Player of the Year twice and was an elite scorer, yet many younger fans know little about him. That lack of recognition is simply a product of time. Players from older generations can become underrated simply because fewer people have seen them play, and because they aren't famous.