I've recently started using Lighthouse to test sites for accessibility compliance, and you can easily get a score of 100 without actually addressing all the accessibility issues a site might have. So, if you're not conscientious, you can just point at the score and say "all good" while your site might still have major issues.

I assume the same is true of the other checks Lighthouse does for performance, best practices, etc.

Lighthouse and other such tools are a good starting point, and using them is better than doing nothing, but a thorough understanding of accessibility etc is necessary to create truly accessible and performant sites.