But the 2016 season provided a natural experiment. The question of how valuable Thomas is to the Seahawks' scheme has been debated often.
His range and playmaking ability have been crucial to Seattle limiting explosive plays over the years.
After Thomas went down with a season-ending broken leg in Week 13, the Seahawks got a chance to see how unique his skill set is and how much he means to the overall scheme. The results without Thomas were ugly.
Even with Thomas on the field, the Seahawks' defense wasn't quite as good as previous years, but it was still formidable. Seattle ranked fifth in opponents' yards per dropback and third in opponents' passer rating.
Without Thomas, the Seahawks had legitimately one of the worst pass defenses in the NFL. They ranked 30th in opposing YPA, 24th in opposing yards per dropback and 31st in opponents' passer rating.
According to Football Outsiders, the Seahawks' defense ranked fifth in passing DVOA through the first 11 weeks of the season (Thomas started every game). From Week 12 to Week 17 -- a span in which Thomas played just one quarter -- the Seahawks ranked 30th.
So what do those numbers mean going forward? Thomas initially said he was contemplating retirement but then confirmed later that he will be back. And Carroll said that barring a setback, Thomas should be ready to go by the start of next season.
But it is concerning that the loss of one player made such a big difference for the Seahawks' defense. Going into 2016, Thomas, Richard Sherman and Russell Wilson had never missed a game. Good health played a significant role in Seattle's success.
That's why depth -- specifically at cornerback and safety -- needs to be a priority this offseason. If the Seahawks lose a key player to an injury in 2017, they need to make sure the dropoff isn't as dramatic as it was last year.