You can still have domain experts collaborate directly with engineers instead of adding a middleman in the form of a product manager.
The more I work, the more I'm convinced that product management is not truly a profession but rather a way for non-technical people to insert themselves into a profitable industry.
The point of a product manager is to make a lot of decisions that don't have a clear answer. "Should we use websockets or REST for our chat client?" - easy technical call. "Which market segment should we target with our features?" - not so technical.
This might make sense from a high level, but again, the devil is in the details.
Realistically you do need someone (vendor or not) to translate 1000's of pages of legal jargon into actual product decisions. There's a tipping point where paying an engineer $x or $y to do that themselves (if they even have the skill to interpret it) is waste of talent.