IMO, the problem with GDPR is the same problem we have with a lot of European laws. There's nobody who's incentivized to enforce compliance.
If you were able to sue for GDPR violations, either on your own or in a class lawsuit, you would have an incentive to prove that the violation has indeed occurred. As long as your lawyer was working on commission, they would share that incentive.
As it stands, all you can do is file a complaint with your GDPR office and hope it makes a difference. You don't get any money from that, so hiring a lawyer to get such a complaint right is an expense you will not get reimbursed for. More importantly, the person investigating your complaint is probably on a salary, not a commission, so they don't personally care about how successful they are.
Compare that to the ADA[1], for example, where you literally get legal firms looking for disabled Americans, finding places that don't comply with the law and suing them. Enforcement was partially privatized, and the free market, as it often does, found a better and more efficient way of enforcing the law than the government could dream of.