Their entire premise is "if you like updates, the S9 is still not going to get them quickly". Makes sense. People who want the latest and greatest should never be considering anything that's not Google or Apple. That's not a fanboy attitude, it's just a perspective most of the market doesn't care about.
The second idea, that Samsung is more secure than stock, is somewhat laughable. It's entirely based on the inability to unlock the bootloader and presence of KNOX, however ignores the hardware and software security differences between the two. As an example, you cannot unlock the bootloader on the Verizon versions of the Pixel 2, etc. and most of the features of KNOX are found in stock Marshmallow, Nougat and Oreo - yet there are security features of Nougat and Oreo that are still not present in the S8 or Note 8. The S9 I don't know if they have caught up yet, but the most important thing about the S9 is that, unless Samsung is going to guarantee 3 years of security updates within 48 hours of public release, and as long as they allow app installation from the Samsung App Store, they will always be intentionally leaving their customers at risk.
I will definitely not be getting the S9, though I am very curious about it's camera - everything else about it is essentially more of the same.