I would suggest this applies to most, if not all, of the others!
We can import/develop brawn. What seems to be difficult to find/build is players with a good rugby brain. For example, I don't think we've ever properly replaced Tom Williams or the Goat.
I think we're closer to replacing some of these players than I ever thought we might. If we look at the 2012 AP Final team versus their closest replacements...
Brown vs Brown (but we don't really have a like-for-like replacement in sight. Could Lang convert to playing there?)
Williams vs Murley (still early days, but I see a lot of Williams in Murley's reading of the game)
Lowe vs Marchant (very similar in quality and reading of the game, though we still miss Lowe's phenomenal defence)
JTH vs Esterhuizen (fingers crossed he could be even better if he lives up to his reputation)
Monye vs Ashton (if he settles into the squad, Ash is arguably even better at reading the game than Monners)
Evans vs Smith (Marcus has a lot to learn but is closer to a direct replacement than we could reasonably expect)
Care vs Care (but, like Brown, we need a successor)
Easter vs Dombrandt (if he can sort his cardio, in time Dombrandt could be better than Easter. And again, the rugby brain is there)
Robshaw vs Clifford (probably... if he can stay fit, Clifford has the brains and physicality, plus a speed that Robshaw lacks. Different kind of player, though, and it's a big if)
Mo vs Chis (different kind of player again, but Chis has a good reading of the game)
Robson vs Symonds (not quite as solid as GOAT, but could get there)
Kohn vs Lewies (Lewies is probably a better rugby player, but we miss Olly's size and impact)
Johnston vs Collier/Louw (the position has changed so much that it's hard to call, even if we'd seen more of Collier or any of Louw)
Gray vs Gray/ Elia (not as settled, but it's hard to argue that the intelligence isn't there...)
Marler vs Marler (2020 Marler is less dynamic, but better in the scrum and in defence and marginally less likely to pick up a ban)
Man for man, the big gaps are in not having a clear replacement for Brown, Robshaw and Care. Overall, it's a lot rawer than the 2012 squad, not least because it's spent much less time together. But if we can keep that group fit and playing together I think it has a similar level of potential.