Thanks for the detailed explanation!

I'm not sure I understand why making the ESB business critical is an error. I mean, it's a key piece in the architecture of your system (say, like a database would be for an app that uses one). It makes sense that it's critical if it's central to your solution. It's also unsurprising if it requires a dedicated team to maintain and monitor, much like any piece of critical infrastructure would. Am I missing something?

What's the alternative? Multiple ad hoc, p2p, uncontrolled connections and streams between arbitrary components of your solution, of varying quality, and many that require maintenance of different kinds. This works for a smaller software with fewer connections, but how does the effort scale as the system grows?