While perhaps true, what needs to be compared here is read, vs read + write, no? Just writing isnt enough. And then we are at a factor above 2, assuming no thread contention. If there is contention, it can be a lot higher.

While "write bandwidth" is probably not the right term, writes are more expensive because you need to update caches. If you forked you might need to copy-on-write the page before you can write to it.