Lucky the Seahawks even had a chance
Even if we leave the whole Wilson factor to one side, there is still a certain element of convenience -- for lack of a better word -- in believing the Seahawks would have three-peated. Consider how lucky they were to be in a position to win their second straight Super Bowl, never mind a third. (Think about Kearse's crazy catch deep downfield, two plays prior to the Butler pick.)
You can further make the argument the Seahawks were fortunate to even be in Tempe, Arizona full stop. The reality is the Packers should have won the NFC Championship Game. More specifically, whether it be the Packers' wasted opportunities, Brandon Bostick mishandling the late onside kick, or the Seahawks' fluke hail-mary two-point conversion. Green Bay in truth lost that game rather than Seattle winning it.
Returning to the 2015 season, a key aspect of the Seahawks' identity was becoming compromised no matter how Super Bowl XLIX played out. Due to the combination of a loss of form and injuries, Lynch was turning into a shadow of his former dominating self. It didn't matter that Thomas Rawls stepped in and performed well, or that the Seahawks still ranked third in rushing yards per game. The team just wasn't the same without their linch-pin. (Pun intended.)
The Seahawks' offensive was also – whether it be because of or in spite of Lynch's diminishing impact – transitioning to becoming more of a pass-oriented attack. The team was never going to be the same again as they continued to bow to Wilson's requests/demands, and the result was they were never really close again to returning to the Super Bowl. Ultimately, Carroll and Sherman – as well as the likes of Doug Baldwin – have every right to believe they would have three-peated if they beat the Patriots in Super Bowl XLIX. In reality, though, it wasn't going to happen.