Jaylen doesn't fit how an All-NBA player is "supposed" to look. People expect high-volume creators, DPOY centers, uber-efficient iso guys like peak Kawhi. Jaylen is more like the slashing wing version of Klay Thompson: he juices up an entire team hard, and works great when playing with high IQ players who make others around them better.
Put another way: if you have a team of guys who make guys around them better, it's really useful to have a guy who's good at getting made better.
Jaylen wouldn't be the #1 offensive option on any of the title contenders, but he'd be the #2 on all of them except the Suns, and that's really valuable.
Thinking about this more, another way to put this is that the guys with Jaylen's Pointz+Narrative profile are usually floor-raisers and 82 game players, whereas Jaylen is much more of a ceiling-raiser and a 16-game player.
If you put Tatum on the Rockets, the Rockets become decent overnight, whereas I don't know that that's true about Jaylen. We see this in the +/- numbers with Tatum and roleplayers. However, the Celtics ceiling falls dramatically without Jaylen: they're a 2nd-round exit team without him.
His game holds up well in the playoffs: he can make tough shots, he focuses more on defense, etc. The 2018 run was narratively about Tatum, but a lot of that was Jaylen taking his game to a new level once that postseason started.
I think that's what I was getting at in saying he'd be the #2 offensive option on most playoff teams: he dramatically raises the ceiling of any contender without being a floor-raiser himself, much like prime Klay.
People expect ceiling-raiser complementary guys to have really high TS% and be more of shooters (Klay, Middleton), so Jaylen throws off analysis a bit by elevating his postseason game in other ways.
Ironically, all of this is an argument for why he
shouldn't get a bump in All-NBA voting, but it looks like narrative+injuries are going to get him onto the 2nd or 3rd team, since no one is really buying Lauri or Randle over him.