1 has nothing to do with Rails. Rails is a framework, Ruby is the language.

As for 2, I see this as a common complaint, but Hotwire, Turbo Streams with ViewComponent is a really power combination whose full potential is still being worked out.

As for client-side error checking... why? So I have to maintain validations in two places and ensure they always match?

I don't even understand your 3. Rails has no UI. Do you mean the CSS applied to the scaffolding views?