The web as we know it was never securable. LLMs made it obvious. We made a wrong turn somewhere back around JavaScript. Eventually we'll get fed up with the quick fixes and design something better. I don't blame the LLMs for this. I blame whoever made that wrong turn back in the 90's (and us, for not turning around sooner).
You're blaming JavaScript? The language that succeeded at delivering fully sandboxed rich client-side applications better than any other tech? With the worst incidents generally being 'just' various forms of fingerprinting?
Or, if you're thinking server-side JavaScript: would the web have been more secure running PHP and Python?