Application design also includes the dependency tiers that provide the middleware and database layers. It could be that many more people will need to be involved when those services are included. What is true is that each SME is part of a silo.
The project has to consult all these silos. Some are helpful, some are not and there are lots of reasons why No! can be the answer to all questions and suggested solutions. All the silos and all the people involved make the whole project slow and costly. The analogy is the game of Snakes and Ladders.