Comparing the “racism” present on a federated service to that on a centralized one doesn’t make sense. You can say certain instances of the service fail to adequately moderate racism, but there are so many niche pockets of mastodon that most people are exposed to, and moderated by, completely different groups.
To make a slightly more nerdy analogy, it’s like someone saying “the windows desktop experience is better than Linux”. Well Linux doesn’t come with a desktop interface, so that statement doesn’t make sense. Which of the dozens of windowers/distros are you talking about? I’m sure the criticism is fair, but it doesn’t contain enough information to make any real claim.
So it’s not unreasonable for one person to say “I see racism on Mastodon” and many others to say “I never see it”, and not just because of the races of the people involved. “Mastodon” refers to a protocol, not the various ecosystems that use it.
Yeah it’s not a mastodon issue any more than racist speech is an issue with our ability to vocalize as humans.
Similarly, the solution to people saying racist things isn’t for all speech to be policed by a central authority, it’s for societies themselves to learn to identify and reject racism.