Bluesky doesn't even need to exist if being "open" means that every network will merge into the same Eternal September rather than remain something unique and independent.
The way filter lists work on the site means you can easily decide to never see posts or users from threads. The "Profile Labeller" [0] labeller already has a specific filter for threads users.
I'm just annoyed you're still limited to less than ten of them at a time.
It's still possible that it could change Bluesky culture for the worse, for example if native Bluesky content devolves into shallow but high engagement Threads type content as a result of being forced to compete with it. But no use worrying about every hypothetical.