Can confirm that message buses aren't just buzzwords and are literally the only feasible way to combine business systems in the most complex of enterprises. I have seen a messaging domain with over 1000 different event types to deal with. Gigabytes of messages per hour. 24/7/365. Tens of thousands of different system interfaces all talking together using synchronous RPC semantics without experiencing any errors for days at a time. Systems spread across the planet. It's the perfect solution if you have the resources to maintain it.