Obviously, I'm a massive Jaylen fanboy, but I think the only way you move him plus other assets for KD is if you know you're not going to be able to get him to re-sign in Boston.
Otherwise, I fail to see how this helps this team down the road. Is KD still KD at age 36 and 37 and 38? The guy is turning 34 in September. To put that in perspective, he'll be about the same age in 2 years that Al Horford is right now. KD obviously has length and shooting ability that will probably age better, but damn, if I'm watching a broken down KD at age 36, while Jaylen is somewhere else putting up 25+ppg at age 27, I'll be absolutely gutted.
I think the C's running it back with the addition of Gallo and Brogdon are more than a legit title contender. I think they're probably the favorite. Blowing it up to put a team out there with less depth, and knowing that if KD or Tatum go down, you basically have no shot just doesn't seem to make sense.
Again, unless you know Jaylen is leaving. Then it makes a ton of sense.
So I get this but I'd say a few things...
1. If the goal is to win titles, KD gives you a much better chance short term, you trade the possibility he's bad at 38 for rings any day.
2. In terms of depth... I actually think (depending who goes out) that a KD trade INCREASES your chances to compete with injuries. The current team struggles with top end scoring/creation, and if Tatum is out they are toast. KD showed last year, he can drag a pretty damn bad roster by himself, if Tatum goes down you're probably still screwed, but KD has a much better chance of getting you through that than Jaylen. We talk about depth, but really what you care about most is winning more of the matchups of your best 7 guys (maybe 8). The Celtics lost the finals because Curry was much better than Tatum, and they didn't clearly win any of the other top 6 matchups. KD changes that in a way that prevents teams from doing what the Warriors did and just selling out on Tatum and knowing nobody else could consistently create and score.
3. KD will decline over the next 4 years, there is no doubt, but.... he's starting from so high, that a declining KD is probably still going to be a top 10-20 player for most (or all) of that time, the odds of Brown being better than KD at any point in the next 4 years is honestly pretty low.
I get the appeal of the infinite timeline... but that's not how the NBA works... if you don't win now, maybe Jaylen leaves, maybe he doesn't, but you take a step back... then Tatum becomes a question. There is a certain value to the idea of a 2-4 year window of having 2 of the 10-15 best players in the league.
I think the only cases for not trading Jaylen for KD are....
1. You have to gut the rest of the top 6 (which is why I think the deal won't happen, because BKN doesn't really want to move Durant and will stick to high asks)
2. Durant makes it clear to you through his agent he doesn't want to come (unlikely)
Fixed that for you a bit. And that's what concerns me quite a bit. Durant's defensive numbers have steadily gone down in recent years. Lebron's went off a cliff.
Durant will likely always be able to score, but if TL goes down, and guys start blowing by Durant....
Durant might cliff on defense, but until I see it I'm not that worried, neither DARKO nor Raptor has shown any substantial decline despite carrying a huge offensive load and playing on a team with almost exclusively minus defenders, getting into a good system with good defenders and being able to avoid bad matchups will be great for him.