Agreed with your thoughts. Our secondary has the potential not only to be better but to be MUCH better, health allowing. I'm curious to see if we can unlock Tomlinson's skills and leave behind his mental mistakes. That would be big as well.
You didn't even mention that we have the potential for strong improvement on the O-Line as well. If the OL can perform as we hope, it unlocks this offense to be not just good but awesome, health allowing.
Plus we have a slightly easier schedule this year.
The lazy analysis of the Rams is that losing AD will automatically make the defense worse. I've heard that from way too many commentators this offseason. And losing him is a blow. But addition of three vets to the secondary, two high draft picks to the DL, and the normal jump from year one to year two for our many young D players could very easily leave us with a much stronger defense, even without AD.
To me, the biggest ?? on defense is Shula. Raheem took the ingredients he had last year and made a surprisingly good defense out of them, esp later in the year. Shula has a bit more to work with. If he can do the same, this team could be a serious contender.