KNICKS
Harden is a perfect fit to take New York's offense to the next level. Brunson has already proven he's well-equipped to play at an elite level as a playmaker alongside another ball-dominant all-star guard. Both guard can initiate the offense in very different ways that would make it difficult for defenses to adjust to.
Nurkic is a good replacement for Mitchell Robinson at starting center. He offers a lot more offensively than Robinson with capable post moves, passing ability at size, and low volume range to space the floor for 5 plays a night.
Melton is a top level backup combo guard. He's got passing ability, athleticism, and can play off-ball which will be important when either Brunson or Harden is on the floor with him 90% of the time. Perhaps, most of all, he brings elite defensive ability off the bench. He's also more experienced than young guys like Quickley and McBridge.
This trade mostly focuses on major offensive upgrades for the Knicks barring Melton. This is most where they need to improve, but I can see people saying that the Knicks would become too weak defensively. I think that no matter who's on the floor, Tibs is gonna put together a top 10 defensive lineup. The Knicks are consistently top 5 since he was hired and I'd argue that just based on personnel, that top 5 consistency is above what Knicks lineups should be delivering without Tibs' guidance. Randle provides the rim protection that Nurkic doesn't. Josh Hart will continue to be elite on the perimeter, Brunson will hold his own, and the bench unit will only be better defensively with Melton.
76ERS
Dame is a major upgrade on Harden at this point in their careers. A Dame Embiid pick and roll would be unstoppable with massive pick and pop potential. I don't think I need to go too deep into why this good for the 6ers.
Melton is a loss, but would be worth the price and isn't worth keeping for the level of tax bill the 6ers would have to pay for not sending his salary out. Moving him is mainly for tax purposes.
BLAZERS
Dame has asked out and Nurkic needs to go. I don't think they're giving up much if anything.
In return, RJ Barrett, Mitchell Robinson, Isaiah Roby, Evan Fournier, and 4 unprotected FRPs is a bounty worth it for Dame. Barrett will fit when Anfernee Simons is moved. Mitchell Robinson is a good young big with defensive capability which the Blazers desperately need. Roby could have some upside at the 4. Fournier is to make salary match and for the Knicks to dump his bad contract. 4 unprotected picks is what a superstar like Dame should earn.