So for the record, the author of the "pact" has been publishing blatant fiction under the guises of "unverified rumors" and nearly everything you said here falls into that. All of it has been confirmed false by either Meta or representatives of the fediverse who met with Meta.
Meta isn't making any special deals with large servers and basically no large servers have signed the pact. Most of the pact signatories are single user servers or similar, there's a handful of small to medium sized ones, and even those who are defederating Meta will not defederate the servers that do federate with Meta.
Oh, absolutely. Even amongst all of the large servers, which expect to allow federation with Threads, none of them intend to give Meta special treatment. If they can't keep their house in order, they will end up getting defederated.
That being said, the big question will be how open Threads is to the rest of the fediverse. It likely won't include the global federated feed, so the question will be how much Threads users end up interacting with the average Mastodon user. It might end up being we only see Threads users when they either manually know a user they want to follow, or Meta promotes content from folks like George Takei into Threads and we see trash comments on that.
Meta isn't making any special deals with large servers and basically no large servers have signed the pact. Most of the pact signatories are single user servers or similar, there's a handful of small to medium sized ones, and even those who are defederating Meta will not defederate the servers that do federate with Meta.