They will tell you you have to delete it yourself.
Comments are technically not necessarily covered under GDPR after they are decoupled from your account and they have no knowledge that it contains other personal data. (which they do not have to check by themselves, that would be ridiculous anyways)
So yes, you do need to run PowerDeleteSuite and then delete your account via account settings (which then triggers deletion in accordance of Article 17)
Thats why we now have certificate transparency reports and CA-records.
Sure not perfect, but at least with a compliant CA it wont just happen in the dark.
At some point you have to trust someone.