I'm going to be a pain and add some specificity.
It's not that equal opportunity wasn't happening, it's that equal opportunity wasn't producing equal outcomes. Opening up to all applicants and not discriminating on the basis of race or anything else doesn't guarantee that you'll get a representative selection of applicants, let alone of qualified applicants.
Of course opening things up to all applicants and not discriminating on the basis of race or anything else doesn't guarantee that you'll get a representative selection. That part, at least, is entirely correct.
With that said, again, the main part of the rise of DEI that I've been distinctly pleased about is, quite simply, the decrease in actual discrimination as qualifiers. For example, as a gay person who neither flaunts nor hides my preferences on that front, the decrease in "simply being gay is a fireable offense" alone would have been enough to leave me with a distinctly positive impression, and has done so. I, at least, am not asking for additional rights, reparations, or whatever else, either way, just meaningfully equal rights to everyone else. One of the major reasons that I'm especially wary of the anti-DEI push is, quite simply, that it has very significant overlap, political and otherwise, with the efforts to make sure that gay people like me don't get to have meaningfully equal rights, period, and want to bring back the "simply being gay is a fireable offense" or worse crap.
For example... my profession is absolutely not representative. Actuarial science is dramatically lacking in black and hispanic professionals. And it's definitely NOT a case of discrimination - all of the exams are completely blinded, we take the exams as numbers, the graders are not present when the exams are taken and are assigned a random collection of tests with no names on them. Each exam is graded by more than one grader, and if they disagree on the points (some tests have a degree of interpretation when it comes to written answers), the graders confer and come to an agreement. It's not possible for discrimination to play a role in it. But despite all of that... there are extremely few black or hispanic people who even try to enter the field. And although females make up about 55% of the starting cohort for the lower level exams, they fall out prior to reaching fellowship level so that at the end of the day, fellows end up being IIRC about 65% male. Asians are overrepresented by a fair bit.
DEI ended up being adopted to try to FORCE things to have equal outcomes. Which is silly, really.
Sure. As I've noted previously, there certainly are fair criticisms that can be raised about DEI programs and arguments related to them, some of which have and are being raised. Yours, in particular, I've mostly found to be quite fair and reasonable.
With that said, I think that poking back at an earlier bit of discussion would likely sum up my overall position on DEI and a bit more of the larger picture at work. Under the influence of DEI, multiple orchestras implemented measures to eliminate discrimination and base selections solely on actual skill. Some of the disparities in representation dropped notably as a result, but not all. I wholeheartedly approve of this kind of DEI effort and am quite pleased that that DEI effort occured and that the orchestras that did implement it did so. By and large, I expect that those who support DEI in this thread are also pleased about things like this and that that plays a role in their positions. The disparities did not vanish completely and some were less affected than others, though, and a few voices have invoked DEI as they try to argue that orchestras should undo the previous measures and institute a way that will force the outcome into something that they think will be more representative of some population. I very much do not approve of that kind of DEI effort and think that it's entirely reasonable to be unhappy with those trying to push it. It's perhaps also worth noting that, unlike the DEI measures to eliminate discrimination, there was no evidence that those recommendations to force the outcome have actually been implemented. I also think that it's unreasonable to try to use that to tar all DEI efforts, including the ones focused on eliminating discrimination. DEI may have noble goals, which truly should be lauded and supported, I think, but any large scale noble human endeavor will have humans that try to accomplish not so noble things under that banner or forget that the means will shape the end actually reached. Personally, I rather prefer having large scale noble human endeavors, either way, even with the need to guard against such.