Everyone has really good bonuses even if they don't become Director, but I'd argue that Ardern has the least important bonus since if we don't pick him, he only gives us +5 to Military Dice.
If I recall what Grimely said, Ardern is a woman, but that's a detail.
That's something of a problem, since we don't really have any military enemies at the moment. We're planning to solve the war to our east with diplomacy since the GDI is loved by both sides, the Useans are going to be too busy preparing for Ulysses to do much to us, and the Veruseans are several nations away on the opposite side of the world from us.
Notably, maintaining site security is likely to involve some nontrivial Military projects. Random weird terrorist groups showing up with military-grade weapons and doing something crazy are not unheard of on Strangereal, so we'll have at least something for them to do.
Also, I think you may be misunderstanding the mechanics. each potential Director candidate gives us their "not-Director" bonus as a subset of their "Director" bonuses.
We are, in effect, given four 'hero units,' one of whom we can get an exaggerated 'super mode' set of traits from (including at least one additional bonus and in all cases except Ardern a penalty) by promoting them to Director. We don't lose anything by picking any of the candidates, except insofar as a Director with an attached negative will of course affect us as Director when they would not affect us as a project chief.
So there's no opportunity cost for any of the four,
except, arguably, for Raskova. Because while Raskova provides objectively better bonuses as Director, she is also more likely to die sooner as a result, which would cause us to lose her +10 [LASER] bonus that we'd receive anyway even if she's not Director.
Since our project is very laser-centric, being able to keep her [LASER] bonus for, say, 2-3 turns longer theoretically turn out to be worth more than getting the [NUCLEAR/DEPLOYMENT] bonus from making her Director. So hypothetically, her more-premature death
might constitute an opportunity cost of making her Director, if we can't get more traction out of the other bonuses in the time she has left to her.
Of course, Raskova also comes with the potentially significant cost of making us more unpopular on the international scene, but that's not an
opportunity cost; that's just a straight-up downside.