No, the anti-DEI stuff is based on the principle that race is a superficial characteristic that doesn’t change how someone would do the job. So, ipso facto, diversity itself can’t improve the performance of a workforce.

but DEI isn't just about race, nor is the idea behind it that a superficial characteristic makes someone more qualified for a job. DEI addresses the systemic barriers that have historically disadvantaged certain populations (like race, gender, socioeconomic status, etc). DEI aims to give them the same opportunities as their counterparts.

for example, DEI is meant to provide opportunities to impoverished white individuals as well, if they have not been able to afford higher education or have been passed on for various jobs because they didn't have the same internships or experiences that their wealthier counterparts had (which may have hindered their professional development).