Personally I think most of the "failures" out there are caused by organisational issues not technology issues. Namely, marketing departments given all the power

Personally I think most of the "failures" out there are caused by organisational issues not technology issues. Namely, marketing departments given all the power over what the website does and what's bundled with it (trackers, a bunch of heavy/intrusive marketing tools), and optimisation that values increasing revenue above increasing actual usability. (Sometimes these align; often they don't). You can make a SPA that's a joy to use and loads and runs extremely fast. Hardware has never been faster; browsers and application frameworks have never been as good as this (I'm talking about the web stack). It's really nothing to do with the tools or technologies that marketing insists it needs mixpanel, GTM, optimizely, hotjar, FB pixel, smooch, and god knows whatever else in order to do its job effectively.