Without a doubt, both are 100% Toyota responsibility. But after suffering from both as manufacturing manager, design is so much simpler to correct. Quality is a moving target and sometimes extremely difficult to get a finger on the root cause. The cheap excuse for that is always "lack of training".To add, we've disagreed about what is build quality or design failure in the past. I didn't understand it then and I don't understand it now. If it's on the truck off production line it's 100% on Toyota.
One thing with Toyota, they own either one. We fault their design like lack of tow hooks or nor forward cameras while driving and they shrug and say piss-off we want it that way. Until they are ready to change, they don't. These brake lines they admitted were incorrect immediately, so they changed them. Their stubbornness in design is why I never bought one or cared for them, too arrogant. But I cannot deny their longevity.