The last sentence of your comment sounds quite condescending.
But categorization doesn't reduce volume of received messages and it remains more than they can handle.
I'm stating it as a style of how I manage my inbox. It's not some big achievement on my part. It's how I stop from feeling overwhelmed by my inbox. Everyone else can do whatever they want.
It's not like I'm that loyal to Gmail. But I've yet to find an alternative that replaces this functionality that I've become accustomed to. It's why I'm asking so many questions of people in this thread.