My personal list:
It is meta, with history of acting against the interests of their users. (Therefore, avoid incentivizing users to be a part of Threads/meta.)
Threads is not part of the #fediverse. Not all public content is available in either direction; threads users are not usually aware of #fedi responses.
[unsourced/unverified] I am told Threads users see what an algorithm selects for them to see, partially supported by above point.
For me, history is important.
In the #fediverse, every server may choose which other servers they will allow connections. Some servers share blocklists of servers which are poorly administrated, and/or have very different cultural/world views within their community. For example, M Trump's TruthSocial is in the fediverse - servers can connect to it - but is nearly universally shunned due to anti-social activities (bots, attacks both social and digital.)
1/2
Threads partially allows some communication, but they hide the method to 'enable' the fediverse. And they censor messages from outside Threads with some very odd filters, apparently.
And, as I said, they decide what you see. Which is exactly what the fediverse does not.
2/2 finis
I was going to reply but you've done just fine with this
Filling in some details, as this issue keeps coming up
1) for #Threads to say that it's #Federated with #Mastodon is -- in short -- a lie
It's marketing PR buzzwords that no one can prevent #Meta from using
2) Threads posts can under some circumstances be seen on Mastodon -- but they are clones only -- I have about ten of the Threads top brass on a Mastodon #List
Replies to them here do not propagate back over to the original post on Threads --they do not show up over there, and I've checked this dozens of times
3) I have had one Reply here to someone from my List, but when I asked him if he'd seen my reply over on Threads and was replying from over there, or if he'd merely seen my reply on the cloned copy over here, he vanished and never answered
Hope this helps a little -- it's a long and confusing issue,,,