My Mastodon instance blocked Threads preemptively because they were afraid of the traffic driving up their hosting costs so you’re basically just very wrong or lying about this. A huge flood of incoming traffic can be hugely expensive for ActivityPub node operators. The problem of giant onboarding events is real, there’s just no default protection against them in Mastodon like there is in Bluesky, so operators either have to take matters into their own hands with defederation or risk driving their bill through the roof.