On discord there are no 200 individual "they" storing it. It's stored by discord. (Or I guess people could be manually logging their own chats, but that's not the issue at hand here.)
At first pass it might sound like some minor technical squabble about implementation details, but there is intentionality in design decisions. The legal system can not be blind to those.
Discord chose a design that put them in control of the data. I'm not saying the highly centralized nature of their design is bad, wrong, or wasn't the best choice for the product they want to build. What I am saying is that when the legal system looks at the nature of a product, it has to look beyond what's presented in the pretty UI and marketing materials. It will look at the business' processes too.
The design of email means there is an argument for the legal system that gmail is a very very popular post office. That email is a system wherein users have disparate storage areas for receiving/archiving emails, and gmail is one of many organizations that offers users the service of managing their individualized storage area on their behalf.
In the service that is email, there is nothing inherently special about gmail. In the service that is discord, discord is discord.
IRC enables Text & Attachments in text form (ie links)
Email Enables Attachments in visual (html emails)
Discord Enables Voice, Text and Attachments (Asynchronous sockets)
That's all it is. Present a Video, Picture, Voice to your visitor and you've got a new product. Just as facebook,twitter,myspace have been.
Assuming all this is correct, if a GMail user requests their account to be deleted, Google should delete that data.
The difference is in what Discord’s responsibility is.
If Discord claimed to have deleted an account, then they shouldn’t still be publishing a post from a user. Especially if such a post could still be tied back to the historical user id.
I can understand why they’d want to keep the data (sometimes you need to keep an archive of posts for legal reasons - for a limited time). But making an archived post visible to the public is the problem.
If I delete my email account, and/or remove it from the list, there's no expectation that my prior emails are deleted for any of the other list subscribers.
The mailing list archive isn't pruned of my account and everything I ever sent will still be visible.
With Discord, all messages are in the “central archive”, there are no individual copies.
Taking a mailing list as an analogy: If there is a central archive of the mailing list, you can request removal of your messages from that archive, but not from the individual recipients who originally received the message.
1. With email you send messages to a specific, finite list of recipients.
2. With email change of recipient list will not send them past messages whereas once you have access to discord channel you get access to history too.