This but unironically.
If people or bots or the NSA want to keep records, let them scrape and cache 'em.
I actually think it should all be P2P, but that would kill the thin shell of a business model that exists.
It would be perfectly fine if Discord stored messages from users (for brevity, assuming that's personal data), made it searchable and available as long as the user exists on the platform, provided that they specify this as the purpose of processing, and the user explicitly gave informed consent. Should Discord want to perform any other processing besides that designated purpose, they would (again) have to receive the user's explicit, informed consent. Otherwise, it's simply not allowed.
No need to remove messages in such a case. Of course, technically they could process that data for a different purpose than specified, but that's illegal and may eventually result in a fine that can be based on a percentage of total global revenue.
Not profit or loss, revenue. Then suddenly it becomes a really interesting business decision to do other than defined things with the data at hand.
(and something something purpose limitation, data minimization etc.)