A subject access request if you just have a mailing list sign-up would require you to provide the information in that mailing-list sign-up and information of how you have processed it. Nothing more, unless you in fact also store other information on a user behind their back.

So, no, it was not an unsolved issue: Just respond. The court case resolved the situation where a company didn't respond, but the request was potentially abusive. Nothing that and legitimate requests are both solved by simply responding.