Speaking English poorly doesn't imply writing will be as poor. I work in Japan and have colleagues who I'll struggle to communicate with verbally, yet I don't have the same issue over text.
I may make the same grammar and orthography mistakes, but at least there is not an additional pronunciation challenge.
But I do consider myself fluent in English (even if far from perfect). I don’t know if that would still be true to someone not fluent in English
One of my language teachers said babies learn listening first, then speaking, then reading and finally writing, whereas adults it is the other way around: adults find it easiest to deal with writing because they control the context and it is in their own time, then reading because although there might be unexpected constructions, it is again in their own time. Then speaking for the same reason as writing, except timing is more real time, and finally listening is the hardest challenge, because it requires real time understanding of the context.
So I agree that I would expect written communication to be easier to deal with for many non natives of any language.