I haven't really looked at the fastrender project to say how much of a browser it implements itself, but it does depend on at least one servo crate: cssparser (https://github.com/servo/rust-cssparser).
Maybe there is a main servo crate as well out there, and fastrender doesn't depend on that crate, but at least in my mind fastrender depends on some servo browser functionality.
That means that SSIMULACRA2 does not capture quality perfectly.
Note that in that figure the formats are compared at the same SSIMULACRA2 score, not at the same file size. In the "very low quality" category, JPEG uses ~0.4 bpp (bits per pixel), while JPEG-XL and AVIF use ~0.13 bpp and ~0.1 bpp, respectively, so JPEG is roughly given 4 times as much space to work with.
In the "med-low quality" category, JPEG-XL and AVIF use around 0.4 bpp, so perhaps you should compare the "very low quality" JPEG with "med-low quality" JPEG-XL and AVIF.
After reading your comment, I assumed you had missed the bpp difference. Please excuse me if I assumed incorrectly.
I realise that a good portion of the references to the product on that page is just "Microsoft 365", but other parts seem to include "Copilot" in the product name for Microsoft's office suite.
This reminds me of the PIK image format (a precursor to JPEG XL) whose name happens to be a word for penis in some languages[0]. In the present case "SPH" is a kink/fetish term meaning "Small Penis Humiliation"[1]. I don't know how many people would think of that, though.
I am not sure if the lesson is to try harder to avoid offence, or live with the fact that words can have multiple meanings and we can be "professional" enough to ignore some of those meanings in some contexts.
Maybe there is a main servo crate as well out there, and fastrender doesn't depend on that crate, but at least in my mind fastrender depends on some servo browser functionality.
EDIT: fastrender also includes the servo HTML parser: html5ever (https://github.com/servo/html5ever).