Honestly, Roblox shouldn't even bother trying to perform validation of Discord or other 3rd party platform messages, as that is just not a scalable approach. Instead, they should ban anyone user who sends any message in-game which includes Discord (or other 3rd party service) link or Discord profile name. Then, they can use such reports from users to manually review if user X has ever said any messages that are sexual, include Discord/etc links and then ban appropriately.
Can you at least agree that we should ban anyone who is trying to engage with children off-platform, even if you don't necessarily agree with using Discord message screenshots as evidence?