The Thumb has a short upper horn, so depending on your playing position, the bass may want to hang at an angle that's no what you prefer. That is a *design* issue, not a *quality* issue. If a bass doesn't have a design that suits you, don't buy it, but don't complain about the "quality".
I had a broadnecked Thumb 6 that I liked quite a bit and never had a problem with neck dive, but I also play with the bass fairly high (which helps my left hand with wide necks, but also puts the weight of your right arm onto the body), and had Dunlop strap locks (which extend the position of the strap and a bit). But if you play with the bass lower and want it to hang at a 45-degree angle, you probably wouldn't have liked it.
Nailed it! Use a decent strap and don't hang the thing down by your nads. Neckdive resolved. Never had this issue on any instrument.