Implementing right to erasure is part of the GDPR. But guess what?
Not sending people’s PII to third parties (whether that be Discord or whatever Discord Webhook Proxy you’re using) is also part of the GDPR.
Do you have the informed consent of the users to send their PII to Discord or a Discord webhook proxy? No? Then don’t violate the GDPR in order in an attempt to not violate the GDPR.
This implementation is just not helpful.