When optimising a title, you are looking to rank for as many terms as possible, without keyword stuffing your title. Often, the best bet is to optimise for a particular phrase (or phrases) – and take a more long-tail approach. Note that too many page titles and not enough actual page text per page could lead to doorway page type situations. A highly relevant unique page title is no longer enough to float a page with thin content. Google cares WAY too much about the page text content these days to let a good title hold up a thin page on most sites.
If you are improving user experience by focusing primarily on the quality of the MC of your pages and avoiding – even removing – old-school SEO techniques – those certainly are positive steps to getting more traffic from Google in 2019 – and the type of content performance Google rewards is in the end largely at least about a satisfying user experience.
Your SEO keywords are the keywords and phrases in your web content that make it possible for people to find your site via search engines. A website that is well optimized for search engines "speaks the same language" as its potential visitor base with keywords for SEO that help connect searchers to your site. Keywords are one of the main elements of SEO.