The fact is that there are demonstrably under-specced batteries being sold. (https://www.youtube.com/watch?v=qMZuHMlRw_0&t=579s)

Is this just a case of people buying reputable batteries and selling them under their own brand name with higher specs? If so, why do these 7 manufacturers make bad batteries?

Clearly there are plenty of badly made cells out there, so I think I'm misunderstanding something.