I very much agree with you - I would use more fans on the outside enclosure, possibly behind more barriers so the sound is never direct (it has to bounce off walls before getting out). Eg a vent cover on the outside or simply vents mounted inside the case (not directly on the outside hole).
(Possibly also keeping the positive pressure inside the enclosure for dust control.)

However there might be an argument about HDD noise that is fairly particular to the drive models.
Maybe op just doesn't like noisy HDDs & isn't that bothered by fans (I centrally am more bothered by enterprise HDD noise than the noise of quality fans), so the solution is HDD-noise oriented (and I think it works in that regard).

(And yes, I do pick my HDDs by noise too.)