They’re garbage at doing this. There is no agreed upon standard of doing it. and because they are so utterly shit at it, all that is left is the appeal to authority, because “our methodology works”.

Not really: most research of any credibility openly shares its data either upfront or on request. The argument isn't "I did this right, trust me, bro", it's "here's my methods & data supporting my analysis & conclusions: check for yourself or even redo it all". Reproducibility (verification of findings) & replicability (same findings with new data) is the standard: once that's done (researchers can communicate to clear up methods or miscommunication), the issues to do that had been cleared up & don't really matter anymore.

A meta-analysis takes in a body of independent studies that replicate findings & analyzes them together to reproduce results, so it addresses both standards.