This is a real thing. Pleroma's reputation on the #fediblock tag is largely "oh god it's another Pleroma with five anime girls who love to nazipost, you know what to do".
Mastodon admins don't see the Pleromas like yours. All we see is the problem ones. Yesterday I saw someone running a single-user Masto who was sharing a bit of code they knocked together to auto-defederate every Pleroma their Masto saw. They said they were fine with losing the obviously vanishingly-small number of non-nazi Pleromas.
I agree that this is fucked up. But this is the reputation Pleroma has among Masto admins. I don't know what Pleroma can do to change this, assuming they want to.