Completely unrelated. Not only are DMCA requests easier to handle than data access requests, the fines for not complying with GDPR are disproportionately larger for violating DMCA.
Work required for complying with a DMCA request: delete the offending material, a basic feature implemented on every single piece of forum software
Work required for complying with a data access request: Search every single service you potentially could have stored user data in and provide it to the user. A non basic feature that requires custom development.
Additionally any malevolent user (as is shown in this case) is incentivized to send a GDPR data access request while this is not true for DMCA.
I agree however that they are both horrible laws. So if your argument was to show that GDPR is just as bad as the DMCA I agree. GDPR is a horrible law and it is not obvious to me that the law wasn't created specifically to target non European business.