Hi Lynda,
We used to use Google site speed tool but that's been discontinued (for now). Yeah, site download is now a critical ranking factor. Google ultimately wants to rank websites that allow users to get quick answers to their search queries. We found WP tends to load slower with all it's plugins. You are correct; there's a lot more to SEO than just the platform . Seems most developers focus on platform and links these days. Good to see Google is onto the ploy.