Yeah, the point of the GDPR request - the data retrieval request - is to get a copy of all posts and comments, which can then be feed into a script that does the actual deletion. Note - I'm not saying that reddit should not do the deletion themselves - in fact I feel that they should, seeing how hard they make it to do it ourselves with their stupid limits.
Worse, all tools like PDS will give a false sense of security here. You'll see from your profile that you have no posts and no comments left, but then you Google your own reddit username and find a bunch of stuff. (It's actually reddit and not the tools like PDS to blame for that false sense of security.)
It seems to have done the job though
My question is - how do you know? how did you check?