Perhaps the better argument would be that these players (i.e. generally the best players on the court at any given time, whomever they were playing), don't really fit the normal positions. In fact, as I pointed out above, the modern NBA has really broken down positional play. At one time you would have a point guard at the arc, distributing to a shooting guard for the outside shot, a strong forward or center to drive the basket or a small forward to move it to one of those players. Michael Jordan broke that mold in a time where that mold was still dominating tactical thinking.
In the past 5-10 years, however, the game has come to rely on a mobile, smaller player. Draymond Green and Kawhi Leonard are good examples. The screen play, one of the most popular plays in modern basketball, requires both players be able to shoot, since who shoots is dependent on which player the defender pivots to. In addition, these players become important defensively important because of their ability to quickly react to fast movement of the ball. It's not coincidence that both of the players I listed are considered top defenders, despite playing forward. Kawahi Leonard has won defensive player of the year twice, and that award is dominated by centers and, to a lesser extent, guards.