The difference is testing to grade the schools and defining tests to measure a standard that all schools must meet. That doesn’t make all of what you said disappear (and that’s an administrative issue) but changing the focus can make standardized tests useful. Regardless of any shortcomings there’s a bigger problem in quality of education in different schools, districts, regions, states and we can’t fix what we can’t identify.

pay and work conditions are not commensurate climbing class sizes, the teacher “shortage” stopped teaching children to read

Those are indeed very likely to be some of the root causes. However if you can’t measure the results you can’t demonstrate you’ve succeeded, addressing all of these doesn’t mean you’ve succeeded, there are most likely other issues to be addressed as well. Standardized testing to measure schools gives a way to identify where things are falling short, gives a way to demonstrate the success in correcting these issues, and gives a way to identify where that is not happening or where that is not enough

As a teacher, you probably can’t do anything about class sizes. As a teacher, if there were anything you could do to increase teacher pay, you’d already be doing it. There need a to be a way to hold a school, a community, a district accountable for a school that can reach a standard bar. That starts with a way to measure whether they are.

You may also argue there are better ways, such as professional audits or evaluations but those aren’t scalable and have not been working.