Doughty has 1 playoff point in his last 5 seasons. His Norris win was 4yrs ago, and he was awful last year. He gets a 'pass' because his overall body or work is great, and he won cups a while ago... but I'm not sure he's the elite franchise Dman he once was. NO, that is not me saying he sucks... it's me pointing out he may not be at that 'franchise' level anymore. Franchise guys put their teams on their back, and win more than LA has in the playoffs in the past 5 years. See Erik Karlsson when Ottawa went to the Finals; McDavid when they went to round 2; MacKinnon this past year; Crosby all the time; and even Doughty back in 2010-2016.
With that said, I'm not sure he's worth 3.000 more than Carlson per season. I think Doughty has the reputation, but if you combine the last two seasons, Carlson has been the better Dman IMO.
It also depends on what you d0 with that 3.000 in cap space...
Doughty + J.Johnson = 14.250
Carlson + Ellis = 14.250
Obviously Carlson and Ellis is a lot better. But the same can be done in reverse to make Doughty's pair look better. For that reason, it's kind of impossible to argue either way.
I think I lean towards Carlson and the cap space, but that's because I believe I could put together a better team by taking the bigger bargain.