Most of the companies where I've had first hand experience test customer experience in the aggregate, ie NPS and similar. Part of this is scale, but a big part

Most of the companies where I've had first hand experience test customer experience in the aggregate, ie NPS and similar. Part of this is scale, but a big part is also CS is viewed as a cost center and it's a rare individual who does what you're suggesting. There's also seldom any sorry if pay off for making that one customer incredibly happy, CS people are not usually tested very well by anyone