I've been in my field long enough where I've seen the same kind of incompetence with and without DEI. The net result is the same.
Pre-DEI it was due to nepotism and candidates being from the same "club", usually social class which includes college connections and plain old geography (right place, right time). With DEI it's most often people not only hired but promoted beyond their ability and expertise so the companies can look progressive.
The difference is that BITD the former group were rarely laid off or demoted, because of those strong social ties. Plus DEI beneficiaries not only receive more scrutiny but are more quickly eliminated because the "club" still runs things. And with the MAGA revolution they don't even have to make excuses.
In other words, even in the face of 2010s-style condemnation, given equal levels of incompetence it's much easier to sack the black woman from the hood rather than the white boy you may be one or two degrees of social separation from. Or he just reminds you of yourself enough where you're willing to cut more slack.
(The Conservative assertion that a free market leads to more rational, profit-based decision making is absolute bullshit, another topic...)