From a contract perspective, it is true that Richardson is less tradable at the deadline with the extension than without it. But he, of course, is more tradable next summer with it. So the question is whether the C’s feel they are more likely to make a major move in February or July.
The Celtics, pre-Richardson extension, already had the Thompson TPE, the Theis TPE, and Kris Dunn’s expiring, which could all be used to acquire a rotation level player to fix a hole, so Richardson’s expiring was less needed. Since then they’ve converted Dunn to Hernangomez’ larger expiring and added the Fournier TPE, so it’s even more true now than it was then. Given that, it would seem that the Celtics feel if they’re going to make a major player acquisition (e.g. Beal, but who knows internally what players they might be targeting) it would be better to have an expiring next summer. And if they don’t make the move, for whatever reason, Richardson is still a perfectly useful player. Maybe paid a couple million more than one would like, but he’s in the ballpark of the correct value, especially with a cap increase that should be 8-10% next year (i.e. less than his raise, so his salary as a percentage of the cap will likely be lower next year than this).
I know you prefer Fournier, and while I don’t miss him, I don’t think you’re crazy. I do think that if the Celtics are trying to make a major move next summer, Richardson’s expiring would be more useful than Fournier in year 2 of a 4-year deal. We heard “flexibility” as the buzzword this summer, and I know a lot of us, myself included, thought that meant leaving room to be a player in free agency next year through cap space. But the Celtics do, in fact, have a lot of flexibility to be active in the trade market both at the deadline and next summer, and when you see all the names that came off the free agency board next year due to extensions, it seems that trades will be how the league shakes itself up in June and July. In the meantime, maybe they have a team that can be competitive — we’ll all have a better idea of that by the deadline — but they have flexibility without punting on the year.
On court, I do think there is concern about Jaylen’s knee/general durability, and I think Richardson’s style of play, while being vastly inferior to Jaylen, is similar, so he can step into that role better if Brown needs a day off. I’m personally a fan of having someone like that on the roster, because it means everyone else doesn’t have to change their assignments and creates a bit more on-court cohesion.