Bitshares instant transactions aren't reliable, because there is only one designated confirmation node for each block period, so the performance of blocks can vary.
Poor performers get voted out, and are no longer permitted to form blocks. Only historically reliable block producers are allowed to mine.
Then it is not decentralized, permissionless. A permissionless system should be able to scale while still permitting slower nodes. In short, yeah you can guarantee anything with total control, but you also insure a power vacuum which is winner-take-all. It is an
Iron Law of Political Economics.
But even your reply is technically ignorant, because the point I was making is that no one can guarantee that a node performs well 100% of the time. Nothing on the internet is perfectly reliable. The fault tolerance must be built into the system by allowing many nodes to confirm transactions simultaneously, not a synchronous queue as is Proof-of-Stake's idiotic design.