"Why every writing company needs a Kenyan Writer"
In theory, I suppose the statements made in this thread make sense...
In reality however, it really doesn't work like that.
I've spent a lot of time 'vetting' writing applicants for the company I used to work for - I've been out of the game for over a year now, but my experience still holds water.
Out of all the applications I've been through, I can think of no more than 5 or 6 writers whose writing lead me to believe they were native English speakers, who it then turned out were ESL writers.
It's all about the details - the subtle nuances in the language that you only pick up by using English with other natives on a daily basis, the sentence structures that just don't 'feel' right.
That said, I've also seen applicants who are native English speakers who wrote junk as well!
Ultimately yes, the question is not 'Are you an ESL writer?', rather 'Can you write native-standard English?'.
Unfortunately, for 99% of ESL writers, the answer is 'No'.