Per PFF, he got the highest grade in his career against the run last season. Wouldn't that be the primary reason the Rams want him?
Durability is also current news. He's leading all D'linemen in snaps at age 31. If he joins the Rams he'll be part of a rotation and that number is sure to come down.
But...back to the main point. None of this is relevant for our context of greatness.
For some reason you decided to challenge the notion that he was ever great. I showed HOF numbers to prove that he was. I noticed you're not disputing that which highlights the silliness of the challenge in the first place.
Your words of will, desire, hard work, and unselfishness I summed up in the one word of greatness. Given that he's on a HOF trajectory, or at the very least been mentioned in hundreds of articles on the subject most of which concede that he's a likely candidate if he continues, I'd say his greatness is generally well established (your dissenting vote notwithstanding).
I daresay that there has been no HOF or near HOF player that hasn't demonstrated a high degree of some combo of will, desire, hard work, and unselfishness. Those internal, intangible qualities don't leave you just because you get older.
So yeah...I'm still going with I feel he has enough will, desire, hard work, and unselfishness to successfully transition to NT. And so does Mr. Phillips!