The Nets are this good because their GM had the courage to mortgage their future (again) for Harden. They'd still be good without Harden, but they wouldn't be as good. Sometimes you just have to pull the trigger. How much different does Boston look with Harden as top billing and Tatum as 2nd fiddle with Walker, Smart, Thompson, R. Williams, and maybe Theis, Teague, Nesmith, Langford, G. Williams, etc. If Boston would have pulled the trigger on a Harden/Brown trade (with Boston sending some picks), not only is Boston is a lot better, but Brooklyn is a lot worse. Plus, Boston still would have had the entire TPE to use for players (so like if Smart was included in the Harden trade, you could still have brought in Fournier).
There is a reason I wanted Harden. Harden is a legit top 5 talent. Add to him a top 15 talent in Tatum and a top 30 or so talent in Walker with 4 or 5 solid rotation players, and you have all of the makings of a championship team. The team as currently constructed just doesn't have the top end talent you need to compete. Harden would have changed that instantly.