You can manually copy locally the content you may need

Why would I, it's online, I know where to find it... until it's gone from there. Also, that would meen I'd have to archive it before I actually needed it archived. And archiving would have to be done manually. And after it's gone, and the only proof of it existing is a text somewhere else saying that the solution to my problem is here -> LINK and the link is that, the data is gone. Not even on archive.org.

Have we really come to a phase of internet use, where everytime you see something, you have to manually save it, and on every post (even here or on reddit, facebook r wherever) a link is not good enough, but you have to copy-paste the whole block of text just to make it a bit future-proof?

we never left that phase dude.

Yes, whatever you see on the internet is temporary. Save it if it matters because at some point it won't exist.