The original intention of the web was to make hypertext documents available to people - PDF is just as valid of a format for this purpose as HTML is. Perhaps more inaccessible but certainly not antithetical to the web.
The single biggest difference is in the text flow algorithm. In PDF it's fixed.
If PDFs feel slow or clunky, that's just a matter of software rendering and payload construction.
The web could benefit from additional text flow algorithms. We leaned into the "application" centric web, but there's so much more we could do for documents and reading.
PDF isn't (hyper)text. HTML (HyperTextMarkupLanguage) is. PDF is blob.
application/pdf
text/pdf.