Unfortunately, blockchain technology cannot be called 100% invulnerable. Don't forget the common "attack 51". This could be very serious.
There are some ways how hackers can intrude in our account, but it wont be unnoticed. By the way, there are good ways to protect your data
You want to say that all data is not stored in the cloud, but in the blockchain? For some reason, it seemed to me that the company's product goes parallel with the blockchain technology. For example, buying access business for cryptocurrency and company tokens. I think you are wrong, correct me if I misunderstood your idea.