Détails additionnels:
For Brent Burns in his heyday, this would have been an absolute steal, but Burns is now 37. Despite that, he's still more than capable of being an elite defender with 54 points in 82 games last season, including a whopping 26:00 ATOI. At 4m for the next three seasons, this allows the Senators to still afford their up-and-coming stars while getting an elite, albeit aging, defender.
The Senators would get a great partner for Chabot, who could learn and develop his game from such an experienced player like Burns. Additionally, Ottawa would get out from under the remaining 2 years of Zaitsev's contract, hence the inclusion of Kleven's rights.
Understandably, Ottawa doesn't want to surrender the 1st Round pick this year or next, so the compromise is giving up the 2nd in 2023 instead.
I compared this to the St. Louis trade when he was 38; St. Louis for Ryan Callahan, a 1st, and a Cond. 2nd.