This post makes certain assumptions based on information taken from Telegram chats. However the conclusions are based on assumptions that are not substantiated by facts are often false.
Yes there are 21 Block Producing nodes, however there are many other nodes that have a full snapshot of the Blockchain that are not producing blocks. You would have to hack 51% of all full nodes on network to compromised Blockchain that is way more then 121 mentioned.
Next: statement that any computer running on IP address can theoretically be hacked is just a theoretical assumption that has little practical utility.
Same goes to quantum computing. If invented - it will compromise all existing encryption standards. However we are a long way from any practical implementation.
I will not address every point in this post but will let community respond.