The Ninth Circuit, by contrast, thinks that such a sentence is just fine. The panel thinks this sentence is by no means "grossly disproportionate" to the offense.
I can't help but wonder whether the experience -- including but not limited to the location -- of the underlying judges might explain at least part of this intellectual divergence. The district court judge, Michael Hogan, has lived in or around Portland [and Eugene], Oregon nearly his entire life, and grew up in Oregon City, Oregon. His experience with the wilderness, including but not limited to fires therein, might be starkly different than, say, the author of the Ninth Circuit's opinion, who was born in St. Louis and who has lived a large portion of his adult life in Detroit, Michigan. Presumably there are far fewer ranches, controlled burns, and wildfires in Detroit than in Oregon.
So maybe that explains part of the dynamic. The fact that the author of the panel opinion spent a great deal of his adult life as a U.S. Attorney might explain a portion as well.
I'm sure there are innumerable other relevant factors in play as well. But my guess is that Holmes was nonetheless onto something when he famously said: "The life of the law has not been logic; it has been experience." Including but not limited to here.