Sucuri writes about their pov on performance:
Whereas Neil Patel writes:
When you’re in the weeds of optimizing your site speed, play smart. Instead of trying hard to push down your document complete, start rendering, or fully loaded page load time metrics (all of which are important), focus on the highest-impact metric first: TTFB.
Where TTFB = time to first byte. Needless to say I’m with Neil on this!