This is implicitly recognized by allowing internal assessment: That assessment would be just as vulnerable to flawed methodology and therefore flawed decision making on products. If you were that concerned over such issues, you could issue further restrictions on performance assessment that limited such activity to be conducted only under Atlassian's close review or using your own mandated methodology. One reason you probably don't do that is because potential buyers would balk at those restrictions and either pass on your product or responsibly engage in due diligence and perform their own assessments regardless.

Further, the resources to do extensive internal assessment may be lacking in many organizations, which means your provision to allow internal testing is meaningless to many customers. As a result, the prohibition against public disclosure thereby deprives them of any way of obtaining objective external analysis.

You could satisfy your concerns by requiring that public disclosure be reviewed by Atlassian prior to publication. You could require an option for Atlassian to comment on the results with embedded notations without restricting publication itself. That would still be heavy handed but at least allow a reasonable amount of independent review of your performance.