How do NBA draft players compare?

Do professional tests, scout observation and analysis while playing, strength training and so on. . . . .

Why are most of them centers and power forwards! Personally, I think it's because the NBA now lacks good players inside! There are few qualified C and C, PF. Most of them are swingers, and some C and PF height are problems. Therefore, the team urgently needs to put it bluntly, it is an idiot talent! Just like a rocket, Yao Ming's replacement is Uncle Mu, who is X years old. . . -。 -Why? Because there is really nothing that meets the salary space (to put it bluntly, the Rockets have no money-) and talented low-post defensive talents! It can be seen that the demand of C and C, PF.