It is very difficult to get the driver included in the upstream. This is why almost none of the Chinese equipment manufacturers do this. And those that do do it for one or two models out of 2-3 dozen produced, and this process rarely takes less than 2-3 years. That is, by the time the device is included in the kernel, it is usually already out of production for a year or more.
So don't repeat these legends from 20 years ago. However, this may not have been true even 20 years ago.
And yet, it's the case for plenty of manufacturers.
Yes, bad driver implementations that shit all over the kernel tree just to get hardware "working" should not be upstreamed. 99% of the time in these cases, Chinese equipment manufacturers can't be bothered to write acceptable code and it's a good thing it isn't mainlined and made someone else's problem.
So don't repeat these legends from 20 years ago. However, this may not have been true even 20 years ago.