Semi-ephemeral is the wrong way to view Discord et al. It's only that way if you actively remove your messages after a while, but they have made it as difficult as possible.

Though the fact that it's hard to archive too, perhaps make it more ephemeral on the whole, since few people will have a backup when do you get around to remove it.

Agreed. This is mostly mitigated by using a Bot to auto-delete all messages in a channel based on time since the post. I've switched to this method to be more ephemeral and have less concern of retention in perpetuity by Discord's egregious privacy policy.

Here is the bot I am leveraging: https://eazyautodelete.xyz/en