Despite the "Gold-suite" comparison, when looking at the KaTeX and RaTeX output [1], the KaTeX output is consistently better. RaTeX has either a lot of aliasing going on or appears blurry.
But the native and library nature of RaTeX is very interesting, especially with the provided C ABI.
Are you viewing on a HiDPI monitor? I imagine this is mostly because RaTeX renders to an image whereas KaTeX is rendering HTML, so can scale to arbitrary dpi. I imagine the RaTeX people could have rendered to a higher resolution and it would look better.
But the native and library nature of RaTeX is very interesting, especially with the provided C ABI.
[1] https://ratex.lites.dev/demo/support-table