Then again, anyone that claims all birds neck dive is making a gross over statement without sufficient experience or data to back it up
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Mine (anniversary issue) doesn't have a hint of neck dive. It stays right where I put it (about a 30 to 45 degree angle). And for the record I only own one non slip grippy strap which I never use because I hate grippy straps, all they do is pull my shirt around (bought it to correct a neck diving Fender and eventually sold the Fender). All my straps are Levys leather bass straps and all have smooth leather on the inside, not suede or anything grippy. I do wear my TBird low, around the waist as opposed to up under my armpit in Jazz bass territory. One could claim that I've just been very fortunate with my TBird, however I have tried about a dozen other Gibson birds all from the late 1990's on and had the exact same experience.
Are there Birds out there that dive? I assume so. Is neck dive an inherent design flaw in modern (non vintage) Gibson Thunderbirds? Nope.
Full disclosure: I have never tried any vintage Gibson TBirds, nor have I tried any Eppiphone Birds or any five string birds or any of the countless "off brand" birds (except my Spector). I have also never tried a nylon strap (because I've never seen one that remotely appealed to me). And for the record I own and regularly play well over a dozen different Fender basses vs my one TBird so I probably don't fit the Bird fanboy profile.