Holmgren was done as an elite coach in the NFL, Holmgren even admitted that himself. He said he no longer understood the game like he used to. It was time for him to step away from the game.
I'm arguing that is where Carroll is now. When he came back into the NFL he defined the defensive meta in the NFL for years. His defenses even spurred rule changes. Now, Carroll is struggling to catch up with the modern NFL. Our defense hasn't been good for years now, and we've been unable to adapt our defense to the modern NFL.
Carroll isn't it anymore. We're going to keep floundering, maybe getting into the WC playoff spot, playing second fiddle to the Rams and 49ers. He's done as a top tier coach. He's also going to be the oldest coach to ever coach the game next season. We can't hold onto him forever, we need to start thinking about the future and whether or not Carroll fits into that future, which I don't think he does at this juncture.