I used the qualifier arguably for a reason. I'm not saying it was the best defensive stretch in history; I'm saying there is an argument. Here's the argument: Seattle had the #1 defense for four straight years and top 5 in six straight. The only other teams that match/surpass that streak are the 50s Browns and the 80s Bears. Best ever? Probably not. But unique enough that Pete almost certainly makes the HoF.
The problem I have with these all-inclusive statements like
"best defensive stretch in history" is that it's comparing apples with oranges. First of all, how do you measure defensive performance, by total points or total yards? And what defines a stretch? 3 years? 5 years? 8 years? You can change the definitions to fit your narrative. And is it fair to judge a 16 game, 32 team league with a 12 game, 16 team league? Are you going to consider teams in the CFL, the old AFL, or the AAFC when making such a statement? Heck, it's a challenge even to find statistics and rankings going back into the 20's and 30's. IMO it's pointless to even argue about it.
If you want to say best or one of the best in his era, I can handle that. You start leaving it open ended by saying best or one of the best in history, you'll always raise the hackles on my neck. More so than baseball or basketball, professional football is way too dynamic for us to compare players and teams from different eras and judge one as being better than another.
Back in 1999, I got a real belly laugh when ESPN named a contemporary, active player in Michael Jordan as the best North American athlete in the 20th century, elevating him over Babe Ruth, Jim Thorpe, et al. They probably owned stock in Nike.