That you clearly a competent operative had trouble with the thing continuing to come loose when reasonably tightened to the point you needed to go OTT, suggests I suspect the design was not fit for purpose.
That's a valid argument, and it would probably win in court, but the honest truth is that I did it up too tight, which I knew at the time, though I was still surprised when it broke.
The point is, though, that there are many ham-fisted owners, who take it upon themselves to adjust their bike. Some even get the brilliant idea to use a higher current charger to charge their battery faster!
It's not just owners either. I had to replace a motor when a guy took his bike into a cycle shop for a puncture repair. The eagle-eyed mechanic spotted the loose disc when he was doing it, which he diagnosed as being caused by the crappy Chinese fixing screws, so he decided to make it better by fitting some nice standard star screws, which are 5mm longer and went straight into the motor rotor.
Then there was the cycle shop that didn't like the wire holding the back wheel after he took it out, so he cut it, fixed the puncture and gave it back to the owner with the wire still cut.
The best one ever heard was when a young guy bought his first motorbike. The dealer showed him all the normal things and handed it over to the guy, who jumped on it and rode of with the motor screaming in every gear. When he brought it in for its 500 mile service, the dealer asked him why he did that. His clever mate had told him that you're supposed to keep the needle in the red band. If the motor had blown up or started smoking 9 months later, should that have been covered by warranty?