I haven't seen ONE good argument that neck dive is a "design flaw". I've only seen people say "I don't like it". Ergonomics, just like tone, appearance, and playability, is a SUBJECTIVE factor.
Let's review the definition of ergonomics: Design factors intended to maximize productivity by minimizing operator fatigue and discomfort. So, you're dead wrong: many of the things I cited: neck profile, string spacing, scale length, and even roundwound strings, directly impact operator fatigue and discomfort. Some bassists say "I'm not entirely comfortable playing 35" scale, but I do so because I feel it gives my B string better tone". So, it's equally reasonable for someone to say "I'm not entirely comfortable with neck dive, but I accept it because I love everything else about the bass".
If you're going to say that neck dive is a design flaw, then you can also say that an excessively heavy bass (whatever that means) is a design flaw. You can say that any bass that you have trouble playing, regardless of the reason (fat neck, number of strings, etc etc etc), was designed poorly... but that's for your comfort, not necessarily everyone else's.
Again: heatheroo's T-bird doesn't dive because of the way he plays it: it doesn't impact his comfort at all. So, one cannot say T-birds (or Thumbs or whatever) have poor ergonomics, even though they neck dive for some players.