No getting cute over-thinking it with additional pieces.

-Pinto is worth more than Laughton.
-A 2nd+Pinto's excess value covers dumping Joseph.
-Flyers are also incentivized to take Joseph, because otherwise, this trade cannot happen due to Ottawa's cap situation.

Ottawa can only afford to sign Pinto to a 1 year deal, which might come in at 1M give or take. They cannot afford cap wise to go 2-3 years, which will take 2.5-3.5 million. To do that, they need to dump Joseph. Dumping Joseph independent of a bigger trade would cost too much in assets.

Additionally, you have to understand that two factors:
1 - Ottawa's window is the next 4-5 seasons while everybody is cost controlled. In 4-5 years, the raises and extensions for Tkachuk and Chabot start kicking in.
2 - Dorion needs to win now to keep his job.

If Dorion signs Pinto to a 1 year contract instead of acquiring Laughton, 2 things happen:
1 - He gets the worse centre this year. This lowers the chances of the team winning in the short term, and Dorion keeping his job.
2 - He has to trade Pinto next year anyways, because he will be eligible for an offer sheet, and if Dorion plans to keep Tarasenko, there will be no room to pay Pinto.

That is very similar to the Zibanejad scenario. Brassard was perceived to be a short-term upgrade who was cost controlled (Salary, not cap, Ottawa was a budget team). Dorion knew his window to win was the next 2-3 seasons while Karlsson, Stone, Hoffman, etc were all cost controlled. He did not care if Zibanejad would be the better player 4 or 5 years down the line. It was a win now move.

Laughton will be cost controlled for 3 seasons, and will be an upgrade on Pinto for at least next year - the return will also be an upgrade on what the Senators might get trading from a position of weakness next year if Pinto goes one year.

I would personally just attach a 1st to Joseph to dump him somewhere, avoid re-signing Tarasenko, and commit to Pinto long-term, but I don't think that is Dorion;s play here. He likely doesn't want to give up another major asset to dump a contract. He will acquire Laughton and justify it as being a big-boy win-now move because other championship teams that may have been Colorado or St.Louis also wanted Laughton.

Ottawa could also take back a 2-way contract to make it 2 contracts in/2 contracts out, but that's not entirely relevant.

This includes the 2025 2nd instead of 2024 because the Flyers already have four top 64 picks in 2024, and I suspect the Senators prefer to keep the 2024 picks due to the depleted prospect pool they have. Although, it could be the 2024 2nd instead, it really doesn't change much.

just wondering why it'll cost so much to dump joseph when he's a 26 year old quick playing 3rd line winger. This seems like a steep price to pay to dump him when imo he has/had more value than then zaitsev and it costed a 2nd and fourth. Im sure the sens can find a trade partner like ARZ, CHI or ANA that could make use of him and not cost us as much.

Term+timing.

It is the worst possible time to dump a contract. It is easier to dump a contract early in the off season while teams still have cap flexibility, or at the trade deadline when some teams who know they are out of it can take on moving parts.

Going by Capfriendly's charts, there are only 8 teams with 3M+ of open cap space. Out of those 8 teams, a few like Arizona might be budget teams, which eliminates them. While this might not be entirely accurate with rosters not set yet, it still shows how few places there are to dump contracts.