The problem for the ACC isn't that they weren't proactive 10 or 15 years ago...it's that they didn't make the right choices 35 years ago when they focused on basketball (in the middle of basketball's renaissance - pro and college) and didn't recognize - along with nearly everyone else - that college football was the future of college athletics revenue.
If you want to castigate UNC for not getting out of the ACC over a decade ago when the media landscape was much different, you're welcome to do so. At that time, though, the differences in conference affiliation was much more limited and the effects of NIL were not really conceived, much less known.
I don't disagree that UNC is at a disadvantage being in the ACC, but a lot of the takes on what "the ACC should have done" is very much monday morning QB'ing with the benefit of hindsight. For a more contemporaneous perspective, see if you can find articles/comments online about Maryland leaving the ACC to join the B1G from 2014-2016 and how their fans weren't happy because they'd sold out for money. (Spoiler: A lot of Maryland fans were lamenting the loss of traditional rivals and a lot of ACC fans were making fun of them for it.)
This is an excellent point, and I would add to it that UNC has historically been a basketball school for 50 years. And part of what made UNC basketball so special was playing in the best conference anywhere. It wasn't only great in terms of talent and success -- it was the entire atmosphere of the conference. The ACC tournament. The rivalries.
Most of us would have been bitterly opposed to leaving the ACC in, say, 1995. I sure as hell would have been.
I think the unexpected factor in all of this was the complete abandonment of the entire purpose of conferences. The whole point of conferences was geographical compactness. It was to preserve regional rivalries; to prevent teams from having to fly all over the country to compete; to offer a balance between competing nationally and regionally.
The first ACC expansion was Florida St. A state contiguous with other ACC schools. Then Miami, same. It wasn't until the mid 2000s that the conference decided that maybe regionality could be expanded a bit -- but the attempt was made to at least preserve the tradition of the conference by adding other quality academic institutions like BC.
Meanwhile, some other conferences decided that TV revenue was all that mattered, and whether the new conference made any sense as a conference was irrelevant. Thus we get the Big 10 -- I mean, sure it's rich, but it can't be satisfying to fans (or players) to be traveling long distances to play teams nobody fucking cares about. Every time I see a story about PSU playing Nebraska in some sport, I feel bad for the fans who have to digest that shit. But then I remember L'Ville and even worse the teams that joined last year (who I refuse to remember out of general principle).
So I think the failure of foresight was not envisioning that college conferences were going to end up like NBA divisions -- mostly meaningless. And that's in part because ACC schools remained true -- at least to some degree -- to the idea of college sports as a complement to the educational experience of college (even if that complement was very large for the best players). Meanwhile, the SEC schools who have never given a flying fuck about academics ruined college sports for the rest of us.