Its a giant safety issue on the road. Good grief, they almost banned hookless in the peloton over this. New rules require strict ETTRO compliance regarding tire size/internal width. So I don't know if was the poster or the rim, but that needs attention.
You're confusing tyres blowing off
over the rim and tyres falling off the bead lock
into the rim well. The latter is no more dangerous than how a normal clincher tyre behaves on a non-tubeless rim when fully deflated. The former is the problem for hookless wheels, and is of course, very dangerous.
In any case, I've mounted GP5k and P Zero Race RS to my XMCS wheels, and they have stayed securely locked when the tyre is flat, even when rolled along the ground in this state. I'd go as far as saying they're the best behaving wheels I have for tubeless considering ease of mounting, inflation with just a track pump, and staying locked when deflated.
Regarding ETRTO recommendations, I have no qualms running 28s or 30s on these wheels because they are
hooked, and the risk of blow off is infinitesimally small compared to hookless rims and tyres of any size. I'll note that Josh Poertner runs 32 mm tyres on his 29 mm internal width 3T Discus 45|40 wheels.
