No, they don't, and the "rarity of the circumstances" thing is irrelevant. These are academic cryptography researchers doing academic cryptography research, and this blog post engages with it as if it was a hostile Consumer Reports review.

The point of this research isn't to make a decision about what messenger you use. The point is to help inform the designers of future, better messaging protocols about what does and doesn't work. Threema's design is littered with stuff that didn't work; it's an important cautionary tale.

You can, according to the paper, send a classic Threema protocol user a message that, if repeated or forwarded, allows someone else to log in as them. That's a distinctively weird and bad problem for a protocol to have. As I said in a comment elsewhere: the Matrix vulnerabilities were much more damaging to Matrix, but the Threema vulnerabilities were much worse as cryptographic flaws. There is more to learn from Threema's failures than from Matrix's.