Sites or "apps" relying heavily on full page loads are, in my experience, much faster than their "efficient" XMLHttpeRequest counterparts, in practice. As in, click, thing happens, thing is done happening, much faster. We even have examples of this with the same "app"—Gmail, for example: Basic HTML, "mobile", standard, and, though I think it's gone now, Inbox. At least four versions. Basic HTML is less janky than "mobile" on mobile, and much, much faster than standard or Inbox, despite "inefficient" full page loads.