Thinking about it from a salary cap position too for those interested, while Erik Karlsson does have a 6.5 cap hit this season, he's also signed into next. "Dylan" as Lil likes to call him currently has a cap hit of 3.9, but as we know he's a upcoming UFA and he'll be making no less than 7 mill from UFA in my earnest opinion. We'd still obviously have to give up more off our books to make a deal work for this season, but upgrading to the better Karlsson would still technically save us money next season pending on if we resigned John Carlson imo.
That said, Erik probably demands no less than 8 maybe even 9+ after that. Especially if the salary cap goes up. It's a big reason why he's rumored to even be in trade talks, Ottawa isn't a team that likes to spend to the Cap as they have a more money tight owner. Combine that with them going into rebuild and it just doesn't make sense to throw 9-10 mill at a big name player like that.