> We like tools, so we start using them, spending days to get the maximum value out of the free ones, spending a lot of time.
> Right? Wrong.
> I have a confession to make: I never used a keyword tool. I do not currently use one, and I find that just thinking about it bores me.
I don't use keyword tools myself but I do think on-page/technical SEO is important. You're not going to rank well on Google with perfect on-page SEO + awful content but if you've got well written content then good on-page SEO can only help. On-page SEO helps Google understand the content better.
I have my own project/tool that checks technical SEO [1] where I've intentionally stayed away from adding any checks/recommendations that aren't backed up by something Google says. I avoid any advice that's based on trying to reverse engineer however Google search works today that could change tomorrow.
For example, I recommend every site is checked for broken links (it's easy to miss broken internal links as you make changes), badly named URLs, missing image ALT tags and duplicate pages+titles (this one is really ease to miss without a crawling tool). You can still rank well even if your site has these problems but SEO fixes like these can only help. Obviously you need to prioritise fixes against time you could spend writing more content but there's a lot of low hanging fruit with on-page SEO.
[1] Rules checked are here https://www.checkbot.io/guide/seo/