or is this oversimplifying the issueIt's oversimplifying the issue. Sealed spkrs will have a higher F3 than the, otherwise identical, ported design but fall off there after with a shallower slope. POrted drops faster.
There are many other considerationa, one of which is that ported design used to be notoriously badly designed. THis is no longer true -- or at least, it doesn't have to be true. You can compute the port parametres (for those designers who are too lazy to do the math -- or can't, which is more often the case).