Everything
@padraig (u.s.) says is true, except this "B/B- supporting cast business around the core." Wiggins, Looney, Poole, Porter, and GP2 are not a "B-level supporting cast." Three of those guys are the second option on most teams—OP had 18PPG on the Wizards, Wiggs and Poole put up similar numbers now. All three are near-max-contract players. Two of those guys are elite defenders, and Porter/Looney are solidly above-average, esp relative to their contracts. In other words, the core trio has
three supporting members who could plausibly get a maximum contract in coming years. That's A-level support IMO, even if health/injury issues have frequently pushed it into B-level (e.g. Lee, Bjelica, Moody subbing in as a result).
Boston may well have the best set of wings in the NBA, but worth pointing out—Thompson/Wiggs isn't far-off. Both are monster, all-NBA caliber defenders. Their combined PER is only a few points behind Brown/Tatum and I'd imagine per-possession efficiency is slightly higher.
I think you're right that Iggy's a big loss, but maybe underestimating Wiggins defensively. Wiggs did a very impressive job, I thought, on Luka, who's notoriously unguardable. Led to a
lot of driving + passing out, which, if Mavs could hit their open 3s, might've actually forced a G6/7.