If someone hired someone provably less qualified that would be easy grounds for a discrimination lawsuit. The problem is actually usually the opposite. People from disadvantaged groups often have to work way harder and be way more qualified just to be treated equally in society.

DEI isn't about who we hire and fire specifically but about how we as a society of institutions act overall. People in DEI might review the hiring and firing practices more holistically as one part of their job. Possibly focusing on recruiting practices including all communities (who are you advertising the job to?), job descriptions being simplified and more honest to what is actually required (broadening who qualifies), training hiring and firing authorities about unconscious bias, etc. That enables them to follow the eeoc laws and truly hire people that are most qualified while having a more representative candidate pool, resulting in a more representative group of employees. When you're correcting your hiring practices to be more equitable, you don't need to hire people less qualified.

DEI would also be how they are treated once there, how the organization treats their staff in a fair and equitable manner. How current policies and processes can be changed to remove structural bias. How to best utilize a broad range of perspectives to improve your organization. For business often how you can include a broader range of targets to market to, etc. Analyzing the structure as a whole for institutional bias. That's all DEI.

The right has perverted the concept of DEI to make people believe unqualified people are landing positions when that's not what DEI is even there for.