This is my side project, I'm a dev currently contracting at DfE. This library and the form builder[0] make working with the design system easier for Rails devs.
Well, why not? It's a great host with a whole bunch of features you'd have to invent yourself otherwise like feature branch previews. It's a static site/documentation site afterall.
former netlify employee here. all sites on netlify have a netlify subdomain, that doesnt go away when you add a custom domain. its just useful for deploy previews and stuff, content is basically the same. nothing untoward here
You have to remember who this is being designed for - citizens wanting to use government services, who may not necessarily have great eyesight, great computer literacy or even literacy in general.
The last thing you should ever want is for someone to fail to apply for welfare benefits because they were overwhelmed by the website design.
I agree that the cookie banner could be smaller though.
The Design System is here: https://design-system.service.gov.uk/get-started/