Intact doesn't mean they will perform the same. Some years players get worse, some years players seem to do great for no reason.
And again, if you're basing it off past production then by the same logic our line should be the best. Past production of our players indicates that we'll have the best D line, even if some of those players are new to the team.
You're trying to split hairs here, and that's cool. I would bank that it's rare for a unit that stays in tact (same players, same coaching staff, etc) to experience a significant drop in production over the course of a season, barring injuries of course. The fact is, our newly tooled defense hasn't played together. Philly, Minnesota, Jacksonville, etc. have.
Nobody wants to bring it up, but teams win on paper all the time, a la Philly back in 2011. I think it's kinda silly to compare a unit that hasn't seen the field together competitively to units that have already had success. But that's just my opinion.
Potentially, we have one of the most dominating defensive lines ever assembled. And if that's how the poll was written, I'll stand corrected. But at this time, our new defensive line hasn't dominated anything but headlines.