I'm not attacking you directly. The line of thinking you're describing is something I've subscribed to myself for the last 20 years and I've at last come to believe its complete fallacy. I understand why it seems logical. And I also understand how that pushes "versatile" defenders who are 6'8" or taller and can move their feet and slide with ballhandlers up the draft board. If I had the free time and the inclination I could make a study and analyze whether this perception lines up with the reality. I'm not going to do that but maybe someone else can. But I suspect the results would show that the do-it-all 1-5 wing defender is a rare exception in the NBA. And even for teams that do have those players, are they substantially better because of it or can other teams get the same results with a 5-player coordinated defense where everybody can switch and defend 2 positions individually?
Forget about size, let's just call Johnson a wing defender. He can guard primary ballhandlers and spot-up shooters. Who's even left in the modern NBA? Which guards are going to take him into the post, back him down, and score over him? With zone defenses, how often are smaller guards getting iso'ed in the post off switches anymore? Look at the trends for leading scorers year to year. If I'm drafting a defensive stopper right now I'm much more worried about containing guards off the dribble and three point shooters than any other type of player.
Theoretically speaking, a player who can guard all 5 positions gives you more options with your defensive rotations but when teams are running 4-out offenses and spotting up even on fast breaks right now, you typically only need to contain 1 or 2 ballhandlers and for everyone else on your defense understanding where they need to be on the floor to cut off passes and take away open shots is more important than physical attributes. I'm seeing a lot of drive and kick and a lot of pick and roll from NBA offenses right now. Smaller players can and do dominate defensively by getting close to ballhandlers and disrupting the point of attack or playing the passing lanes with their quickness and anticipation. Long arms might give you a wider radius to disrupt those passes but how many players take full advantage of their wingspan on the perimeter? Conversely, how hard is it going to be for a 6'8" player to get small and go outside a screen to defend a step back? The phrase "jack of all trades, master of none" may apply here. The "versatile" defender may be above average at everything but a more specialized player is probably better within their area of expertise and maybe that ends up being what impacts the game more?