PMs can help only with one part (the "problem"), but, unless they are also good architects and designers, the end result and the process end up being pretty painful.

The devs still need to learn about the domain and they need to understand it enough to build a good solution. Having to learn a new domain on your own can be tough. Having external SMEs (subject matter experts) reducing the ramp up time and answering detailed questions is a big help.

It's pretty common for PMs not to be SMEs though...