[vincnetas]

"from their coinbase account to my coinbase account" so if i understand correctly this basically eliminates blockchain and leaves you with plain old database in the backed of some provider to keep track of how much "money" you have. And if provider gets hacked well, tough luck...

[MertsA]

If we're talking about Coinbase in particular then yes but you can have secure off chain transactions like Lightning network where either both parties agree or the funds are locked until the channel closes and returns them to the sender.