It's one model. Other models aren't as kind to Carlson, though none paint him as terrible of course. Micah's model, for instance, has the following for Carlson:
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Over a 5-year sample he's been a net drag on 5v5 chance production when accounting for teammates, competition, zone-starts, etc. Particularly bad defensively, and not very good at producing chances offensively (though he is good at finishing chances).
Carlson is good. But he's not a true #1 on a contender. The best we can hope for really is a platoon #1 situation like he was when Niskanen was around, but even then Carlson is only getting older and more dinged up every year. Carlson in particular has been abused over the past 3 postseasons. I don't have any models handy to prove this other than his lack of 5v5 production (both in terms of chances and points), but I doubt anyone is happy with his performance.
Either the Capitals have to find a Niskanen-type shutdown defender to keep Carlson away from any matchup roles, or they need to acquire a true all-situations #1. I suggested the latter with Dougie Hamilton, but now that that has come and gone I don't really see another good option in that direction.