Minnesota is a poorly constructed team. They have a lot of offensive chuckers without any real defenders. Dieng and KAT are a bad mix up front. Rubio, Lavine, and Wiggins just doesn't work in the backcourt. They then hired a defensive oriented coach, that isn't a great offensive coach, to coach a bunch of great offensive players that are terrible to poor defenders. It is just a bad mix of players/coaching in Minnesota.
The Sixers are put together much better assuming they pick up a guard in the draft. They will have a two way anchor at center (Embiid), a solid stretch 4 (Saric), a 3 and D veteran SF (Covington), and two rookies in the backcourt (one the #1 pick in the draft (Simmons), and the other at least a top 7 pick (whomever they land this summer)). Plus they will have some quality vets on the bench in Henderson, Bayless, Rodriguez, with some other young guys that will continue to grow in Okafor, Anderson, Stauskas, McConnell, and Holmes. That also doesn't account for the possibility of getting the Lakers pick and their immense cap space from which they could add talent.
And to be fair, I said if Simmons lives up to the hype (and called it a big if), they would be one of the better teams in the NBA in 3 years. Very good chance he doesn't live up to the hype.