On the point of security of own funds here, blockchain security had nothing in business because securing your own funds is your responsibility because as you said, self banker, so you should need to be aware of the demerits of being a self-banker. For your findings on Blockchain security, the word impossible seems to be more than needed, Blockchain is secure but you should need to be aware of the working of the blockchain consensus algorithm but I had already read you've mentioned that point as well. For the Bitcoin Blockchain, you can really use the word "Impossible" but be aware of the point that the blockchain will be truly secure if and only if it is well decentralized.

If a blockchain is not well decentralized with limited nodes as in most cases where team members own the most of nodes sometimes all the nodes as well, on such type of blockchain you should need to be aware of it that team can directly manipulate the blockchain and your funds will not be secure there. So that's why Bitcoin is standing like King because of its community and strong network.