I've done a GDPR information request for all data related to me. It can take a while. Once I have it, I will go through it as best I can. Most likely, I'll then file a GDPR right-to-be-forgotten request.
If you delete your account, they can still retain all the data, they just take away your ability to modify it. With a right-to-be-forgotten request, either they yeet all your data (should be the same as the information request returned), or they are in violation of law.
Sure, reddit doesn't operate from within the EU, but I bet they'd still like to do business in the EUR zone.