I only see it posted on 3 communities, isn’t that how the Lemmy cross posting feature is supposed to work? What if someone is unaware of 1 or 2 of these communities, or their instance is defederated from 1 of them?
Lemmy has post deduplication. Are you using an app that doesn’t support this? I haven’t seen crossposts spamming my feed before, usually it’s a pretty good feature, something that Reddit doesn’t have.