Simmons has said just that several of the various podcasts he has been on, that the Sixers screwed up by giving him the extension early which left them with no way to trade him.
Philly gets Hayward, Grant, Wanamaker, Edwards, and Green.
Celtics get Simmons, Richardson, Scott, Smith, Burke.
Salaries work*. I’m not sure the resultant teams do, however, and almost certainly Philly needs at least the Memphis pick.
* — Sixers absorb Hayward and Edwards by the 125% rule from all their outgoing players aggregated together, Wanamaker and Green via the minimum exception, and Grant through the Fultz TPE. Celtics absorb Simmons and Richardson using 125% of Hayward’s salary, Smith via 175% of Grant, Scott via 175% of Wanamaker+Edwards+Green, and Burke via the minimum exception.