There's a tinge of "the expectations at Duke aren't the same as they are for Tennessee", which I don't believe is accurate. In fact, I know that it's not accurate.
Kara has done a fantastic job of building Duke back to national prominence*, but what people seem to forget is that Duke had a reputation for her to restore. With that reputation comes expectations. Gail Goestenkors, hands down the best coach in the history of the program, took Duke to two national championship games (1999 vs Purdue and 2006 vs Maryland) and lost them both. That second loss, in particular, accelerated her departure from the program (much of that wasn't her fault, but that's a story for a different day). The expectation was clear--national championship or bust. When Gail couldn't deliver, she was effectively let go (by a clown of an AD). Her successor (the repugnant Joanne McCallie) was good enough to continue to grab elite talent and get Duke to multiple Elite 8s but failed to deliver on a Final 4. Then, her scumbag actions led to the program cratering to the state that it was before Kara arrived.
I say all that to say that the expectations for Kara at Duke are the same as they would be for her if she goes to Tennessee. There are two questions that she'd have to answer in order to choose between Duke and Tennessee. First, what's the best path year in and year out to a #1 seed--the ACC way (where you may have to win at least a share of the ACC regular season AND the conference tournament every season) or the SEC way (where you could get one without having to win either)? Second, what are the resources that I need to get the players that I need to compete with the top of the SEC, top of the B1G, and UConn? Do I need to be in the SEC to get them or can I get them as the head coach of Duke? You yourself said that the path to the top of the ACC isn't as steep as it is in the SEC, so what happens if/when some of those young coaches at Clemson (which has a nice supply of NIL money), Virginia Tech (which is building back football--a move that will help the entire athletic department), UVA (Mr. Reddit, among others, has infused the program with cash so that they can buy players), etc. start putting it together and catch up to Kara's Duke teams? Keep in mind that Jeff Walz isn't going anywhere.
If Tennessee comes calling, Kara better think long and hard about accepting. And if she does, Duke will be fine as long as we can lure back Lindsey Harding.
*I would argue that while Duke is only back in the sense that the team is highly ranked again, Duke, as a dominant force in WCBB, is still not back. We don't have consensus All-Americans and strong NPOY candidates. We haven't made the Final 4 since 2006 (meanwhile, Notre Dame and Louisville have been several times, NC State and Virginia Tech and even Syracuse have been to one). We haven't had a first round WNBA draft pick in forever (no, Azura Stevens doesn't count for us, unfortunately). To truly bring Duke back, Kara's going to have to deliver on all of that. Given how tough the SEC is and how many resources available to the teams at the top of that conference, I'm not so sure that she can.