Buckle up? It could just be a player moving to a bigger house....happens all the time. I remember a while ago Canadiens fans on the trade board were going nuts because Pacioretty listed his house and nothing came of it.
Phaneuf is still a solid player who they've shown interest in and fills a major role for them.
The thing about Carter is, he's turning 33 early this season and has a ton of mileage on his body after all the playoff hockey the King's have played over the last 6-7 years. He still has 5 years left on his deal....5 years. He'll be nearly 38 when the deal expires. The cap hit is a bargain now, but there's potential for him to decline.
With Turris, they downgrade but they get a center who is 4 years younger. Turris will be more expensive to extend if they opt to go that route and they kick the can down the road of having an older player on a big cap hit by a few seasons. They could also opt to trade Turris for a big package at the deadline if they are out of the playoffs again and Turris isn't open to extending LA would be in a position to try and get a decent return for him in the form of picks+prospects.
Carter's age in conjunction with his cap hit is not an issue for the Senators since as far as we know, the Sens are a budget team going forward so the salary is more important than the cap hit. Even if Carter declines during the last 2-3 years of his deal, his salary drops substantially to the point where he only makes 2M for the last two years of the deal. At that price, if he's a responsible vet 4th liner (aka the absolute worst case scenario) he would be earning his contract....obviously the Sens would hope for him to be able to hold up for as long as possible as a top 6 player.
I'll be the first to admit, like a lot of people, I find it very hard to assess "value" in the NHL. So it's entirely possible, the Sens need to add in some form but the Sens adding another asset wouldn't change the basis of the trade and why it works so well balancing the salary needs of a budget team vs LA's cap situation.
Ultimately, LA would be turning Carter into Phaneuf+Turris, two very good players, and then dumping Gaborik to subsidise Phaneuf's inflated cap hit. If anything like that trade happened, obviously I'd be shocked, but I don't think the premise is that outlandish even if I may not have gotten the value right.