But yes, you can never just do what "the users" ask for. The best way to understand what they need is to be in conversation with them. Silo'ing everyone up isn't going to make the overall product -- which has to be composed of all these sub-components working well with each other -- any better.
Oh it absolutely can; it's just that it usually is not a good idea. But I'm not talking about the process of reaching that decision, I'm talking about the responsibility to reach them. Functional and technical decisions are separate, but in most cases should be defined in conjunction.
> Silo'ing everyone up isn't going to make the overall product
This is true for certain types of product, and less so for others; you need to clearly understand what type of product you're building, and be ready to adapt as it changes (or you have a better understanding of it). In a nutshell, the more compartmentalised a product is, the isolation between the teams becomes more beneficial. Which brings us full circle back to Conway's Law.
Of course you're talking about the process. Your claims that "direct communication between teams is not the right method for that," and "communication between teams working on discreet, separate units can become detrimental," for instance, are about process.
I don't think this conversation is going anywhere, but from my experience, lack of communication between teams working on discrete, separate units (that are expected to be composed to provide business value), can become detrimental. And that's about process.
Edit: I just noticed that "PM" in parent comment. Basically, product managers are not just for UI and customer-facing products.