This is a dodge. You can use this argument to avoid doing anything you don't want to do. There are very few things that can be done so well that no one can find fault with the way they were done. While the assessments may not be real good, they can provide useful feedback for improvement of the quality of the educational process. Since all assessments are fallible, you must interpret any results you get intelligently, with a thorough understanding of the context within which the assessment was done, and with awareness of the limitations of the assessment procedure.
Educational outcomes are complex, multifaceted things.
The desired outcomes occur on many levels. You have to use multiple convergent measures to attempt to bracket the outcomes. Multiple convergent measures are complex, and difficult to interpret. Frequently the different measures send conflicting, even contradictory, messages. What is surprising is how often college professors and university administrators can't deal with it.