Honestly, it’s best to just ignore this kind of FUD. Quantum computers are nowhere near a real threat to Bitcoin anytime soon.
You are right that it is not a threat to cryptographic systems anytime soon, but since it is a possible threat in the future, i would not call it fud, because if it were, developers would have have started research on quantum resistant algorithms. However, from the little research i have done about QC, i don't think the threat is 50 years away, i believe it is at least half of that or even less.
I think if QC is not a threat to crypto in the near future, there is no guarantee that it will be a threat in the future. QC only becomes a real threat if its growth rate outpaces that of crypto, otherwise, this threat will still remain theoretical. As you said, QC needs at least 20 more years to reach the power that can harm the crypto industry today but in the meantime, developers have started researching quantum resistant algorithms from now. That means we are still progressing better than them and the gap is still very far. I don't think they can catch up with us to pose a real threat in the future.