I'm not sure if egg-shape falls to my same criticism, though. In fact, I'm pretty sure it doesn't. Imagine being on an egg surface on the inside -- if you look straight across, there are only a couple of places where you're actually looking at a parallel surface (top, bottom, "equator").
Also, one resonance is easier to deal with than three. So it's not like it's a fatal flaw to go with that particular enclosure shape. I'm not sure your first statement makes sense. A dynamic driver has rear dispersion as well as forward dispersion as well, and is figure-8-ish in shape as well. The only difference (and I won't pretend to know more about this than I do, which is well nigh naught) may be that ESL drivers handle back-EMF differently than dynamic drivers do, which I suspect is the case. As to whether that's "better" or "worse", I don't know. But either way, you still have to worry about the signal reflecting and interfering with the forward signal and causing comb filtering, so I certainly agree with your conclusion.