No. There is just a handful of companies producing cells at reasonable scale and cost. Pretty much every cell you can buy from Alibaba (which is almost certainly where these e-bike pack makers are buying from) come from just 7 companies: CATL, BYD, EVE, CALB, Gotion, Sunwoda and Farasis.
All of these companies make high quality cells and these are definitely the only ones with a good enough price/performance to shove in a hand-made e-bike pack and make a profit.
This notion that Chinese batteries are somehow bad is ludicrous and the lengths people go to state as fact something they clearly have no experience with is intellectual dishonesty at best.
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.
Are you serious? Yes, obviously. Spend 5 minutes on Alibaba looking at the panoply of companies selling cheap cells, and reading forum posts from people who build their own batteries unfortunate enough to buy those cells.