I agree that does seem to be something of a smoking gun.

And it’s not without precedent to secure an injunction against as US tech company launching a new service - gmail was known as googlemail in the UK and some European countries for several years owing to a trademark dispute (https://www.theguardian.com/media/pda/2010/may/04/digital-me...)

But sadly a lot of trademark and copyright cases come down to who has the bigger pile of cash behind them.

Could they not argue that Threads was removed from FB because they refused to sell the domain or violated some TOC and not because of user confusion?

That first argument just sounds like bullying and may be anti-competitive business practices. IANAL but I think refusing a specific person's access to your product specifically because they refused to sign a separate contract with you would be seen as a pretty clear case of you abusing your market control and probably some form of coercion. I'd love to see FB declare that - but it's much more likely they'd stick to "Oh, violated our TOS for some reason".

"Oh? What?... Oops, The Algorithm banned your fanpage because it was flagged, wait, let me check, ah yes, multiple reports of trademark violation on behalf of... Meta? Oh that's us. I apologize, it seems our employees were ever so vigilant but didn't know your app is a thing. An innocent false positive, nothing more."

Those reasons sound even worse.

It's not necessary to sound better. All you need to do is win a legal battle.

You're not going to win by undermining the foundations of your own argument, but don't mind me - please pitch this to Meta's legal department.