It took me nearly a week to overwrite my 15+ years of content before I deleted my account. All of the mass-delete tools I tried ran afoul of underhanded Reddit tricks like rate limiting or having my session forcibly expired.
Ultimately I had to fork Power Delete Suite and make it wait 2000ms between requests (and to not overwrite previously overwritten content). That ran for almost two days straight before I was able to confirm that everything was successfully replaced.
But there you have it, I am officially Reddit-free.
RES + developer tools worked for me to delete them until my profile ran out of comments. But a quick Google search found that a bunch of my comments are still there, they just don’t show up in my profile.