Public policies were made (or justified) based on some of this research. People used this "settled science" to make consequential decisions.

Stereotype threat for example was widely used to explain test score gaps as purely environmental, which contributed to the public seeing gaps as a moral emergency that needed to be fixed, leading to affirmative action policies.

To be honest, whether they had a "study" proving it or not I think those things would have happened anyway.

It's just a question of power in the end. And even if you could question the legitimacy of "studies" the people in power use to justify their ruling, they would produce a dozen more flawed justifications before you could even produce one serious debunking. And they wouldn't even have to give much light to your production so you would need large cultural and political support.

Psychology exists mostly as a new religion; it serves as a tool for justification for people in power, it is used just in the same way as the bible.

It should not be surprising to anyone that much of it isn't replicable (nor falsifiable in the first place) and when it is, the effects are so close to randomness that you can't even be sure of what it means. This is all by design, you need to keep people confused to rule over them. If they start asking questions you can't answer, you lose authority and legitimacy. Psychology is the tool that serves the dominant ideology that is used to "answer" those questions.