You've now moved the goalposts from "a discussion about what constitutes "your data" under GDPR" to a discussion about moral rights for deleting accidental content, and a reference to Discord's ToS, neither of which have anything to do with GDPR.
Check the ToS you don't own anything on Discord you even transfer copyright for every word you type. What even is your argument here? That it would be nice otherwise?
This is blatantly false. https://discord.com/terms under "your content" claims that I give Discord a forwardable and nonrevokable license to do anything with my content, not that I transfer copyright.