It will always make the most sense to source the best people without regard to anything but job skill. If the best people aren't diverse, then chasing diversity requires you to look outside the set of best people, by construction. You can't have your cake and eat it, too.
What I have seen in my experience is not a lowering of the bar for more diverse hires, but a lowering of the bar when a company wants to drastically increase its number of engineers. Yet the lowered bar does not increase the percentage of diverse hires, quite the opposite. I've seen lowering the bar for white men, but no other group.
I say this as a white man who doesn't want to work with poor quality engineers who are uncoachable. It infuriates my sense of logic when they cry about not wanting to lower the bar while doing exactly that.
Not to mention, if the other companies also wish to hit their diversity goals, they will be forced to take on weaker hires, since the (already small) pool of adequate hires has been exhausted. In my opinion, diversity hiring is an anti-pattern. Hiring should instead ignore demographics information rather than use it to try and achieve some optimal representational balance. If demographics information are completely ignored in the hiring process (which is impossible if you do on-site hiring), then no one can accuse you of favoring a particular group of people.