The very fact that people choose a mode of working and stick to it says that they are satisfied with their chosen mode of working in all respects. Here in this context of working with 4 or 5 articles at a time has certainly must have suited some. Had it failed in doing justice to the articles they wouldn't have continued with that mode of working.
It depends , some are happy with shorter articles and may nit bother to put in a lot of content and when that is the case you can churn out half a dozen articles in a day - say between 500 - 600 words! It also may be financially sound since that way you are earning more ..
It is very much possible to work on several articles a day, people are doing it successfully but they are not writing them simultaneously, all at a time. I am writing on a site where one is allowed to write 10 in a day (I write 1 in three days) but the articles allowed are at least 400 characters that is roughly 100 words. You can do that ,but even these articles are written one by one, no one starts all of them all at the same time or 4-5 at the same time. At the most one starts one article feels distracted at a point and leave it to finish later.