Why does this matter more than any SEO tool?
Because every third-party tool estimates your traffic and positions. Search Console reports them, from Google, about your site, for free.
The numbers in a typical agency report come from tools that model search volume and infer position from sampled data. They are useful for research and they are not your data. Search Console is measured: these are the searches where your pages appeared, the number of times they appeared, and the number of times somebody clicked.
That distinction is the reason our client reporting comes out of Search Console rather than a rank tracker. It is also why it is the first account we ask for, and the first thing worth setting up if you do nothing else on this page.