That's a strange way of framing things. Anyways, here's some actual evidence:

https://credo.stanford.edu/studies/charter-school-studies

Be sure to read it carefully, and disaggregate the online charter schools from the brick and mortar.

You can't take the stats of a charter school vs its district peers and extrapolate that to the state level. It's also notable that Massachusetts doesn't have a recent report.

I also took a look at the 2019 Washington (my state) press release with the following bullet point:

o School level findings identified several charter schools with significantly positive impacts, as much as 165 and 189 more days of learning in reading and math, respectively, compared to the learning they would have realized in traditional public schools. Conversely, some charters significantly underperformed their local school options by as much as 106 and 83 fewer days of learning in reading and math, respectively

I'm not saying that charter schools aren't useful, what I am willing to say is that charter schools provide a good solution to a particular problem that has more to do school quality being tied to local tax revenue than unions.

I think it's more about options. Charter schools have the freedom to experiment with new ideas, which means their outcomes are likely to be more variable. Some will be better than traditional schools, some will be worse. But over time, that freedom to experiment should converge to an overall higher standard of education. At least, that's the theory, but the data seem consistent with that so far.