is using google analytics to improve seo still worth the effort?

Yes, but GA on its own won't move rankings, it just shows you where to look. The two things I actually use it for: 1. landing pages report filtered to organic search, sorted by sessions, so you can see which pages earn search traffic and which ones are dead weight 2. engagement on those pages. a page ranking well with people bouncing straight off is the one to rewrite Link Search Console into GA4 too, otherwise you have no query data at all. The flattening after two weeks is normal, rankings rarely move in a straight line.