Absolutely not true, I’m afraid. I’ve architected or worked with message bus architectures in large-scale medical payments processing systems, as a central broker for a national-level telecommunications company, multiple Fortune 500 consumer-oriented companies with complex sales workflows, and so on. This doesn’t obviate the need to be clear on producer-consumer relations, as you point out, but that’s a governance issue, not a technical architecture problem, and one that is at least as severe with API-only architectures.