Public libraries are great and there should be a lot more of them and everyone should enjoy them, but they should absolutely not be a substitute for respectful, accessible web design and engineering. The elitism is that only people with the shiniest new devices should get to use your website on their terms.
You are either refusing to address the central point or your reading comprehension needs a lot of work. A premise of your original post was that libraries have newer devices than some users. I maintain that libraries should not have to be a fallback for your crappy website.
Right, and I’m positing that you don’t need to support 20 year old devices that receive zero updates because everyone has access to libraries in an absolute last resort.
There are limited resources when developing software. This is a pretty bad resource sink.
There are types of software for which I’d largely agree with you. Websites are not one of them: it takes effort or incompetence to make them slow and inaccessible.