That quote also mentions a very good reason for which radio hardware makers in particular must have firmware that users can't modify: they are not allowed to sell the hardware unless it is guaranteed to meet all radio regulations. Otherwise, if you use hardware they produced to emit radio in illegal ways, they will be held liable, if they didn't take steps to prevent this, at least in the USA. Libre radio firmware will never happen unless legislation in the area changes significantly.
I also would say, again, that I very much doubt any other manufacturer is getting the kind of specs you are hoping for. Android phones at least definitely use firmware blobs from component manufacturers. Apple does as well for the antennas, though maybe not for some other parts?
> a very good reason for which radio hardware makers in particular must have firmware that users can't modify
This is not a very good reason. By this reasoning, ordinary cars must be prohibited, since you can dangerously modify them. Also, it's not relevant for this discussion.
I also would say, again, that I very much doubt any other manufacturer is getting the kind of specs you are hoping for. Android phones at least definitely use firmware blobs from component manufacturers. Apple does as well for the antennas, though maybe not for some other parts?