Testimonials, despite carrying the baggage of being a marketing term, are a legitimate form of evidence, especially if the people giving testimony are named in full. It affects their reputation if either they or the company they are testifying for are disreputable.
It’s true that independent reporting will be more likely to provide a balanced and objective assessment, but at the same time, opinionated articles like the submitted essay are more valuable with the provision of stronger evidence.
Testimonials in general are like these cheesy or sleazy infomercials on home shopping channels, fake and worthless and that's why they earned the bad reputation that they have.
Also, it is not even that the essay itself is totally bereft of real world examples to support his thesis, when he actually cited Airbnb as a case of coming around, and applying the practical advice given to the founders by YC to deliver value.
To clarify, I maintain that testimonials from people who give their full names (and thus can be contacted after) are perceived as solid evidence. A common real-life example of named testimonials seen as credible by recruiters are written LinkedIn endorsements from named people who are connections on a person's profile. However, I agree that nameless or semi-anonymized testimonials are less valuable and give the entire term of "testimonial" a poor reputation, because their truthfulness can't be verified.
On the second point, what you wrote is true, but the Airbnb mention was pretty short; your comment is probably around the same length as Graham's mention. The Airbnb mention in full consists of: "[4] The Airbnbs were particularly good at listening — partly because they were flexible and disciplined, but also because they'd had such a rough time during the preceding year. They were ready to listen."
I could find no mentions of other named companies involved with YC in the article, and the Airbnb mention was quite brief (the assertion was that they listened to YC's advice, and the implication is that this was the reason behind its success).
1) As you said, these LinkedIn *testimonials" are more of professional endorsements than anything. In my opinions, testimonials on the web have become totally discredited, and the moment I see one in the wild, the first thing that pops on my mind, it's a commercial with an identity crisis.
2) I totally agree with you that details are scarce and left much to be desired but maybe this narrative is more suitable to other media like books or podcasts where they have the space to expand on points and let us all on the juicy details.
I pretty much would have appreciated to hear the full story on Airbnb struggles in the beginning and how they managed to turn it around.
It’s true that independent reporting will be more likely to provide a balanced and objective assessment, but at the same time, opinionated articles like the submitted essay are more valuable with the provision of stronger evidence.