I am not asking anybody to be an expert in both (although I am sure such people exist, however rare); I am saying people should ideally have some skill in both. Also, people can collaborate, and learn new skills.
If you're bottle-necked by waiting for the users of your product to give a feedback, you clearly need to spend more time learning how to be a user yourself. Or hire people with some domain skill who can also code.
I find that this argument is used too often to refrain from using your own product.
Yes you're right not anyone can be a domain expert. But anyone in the company needs to at least try to use the product as much as possible.
I worked in companies where even the CEO had never used the product but was telling us what to implement.
sure 'everyone' drives so you can be a domain expert in cars. However not everyone can be an astronaught - rockets are complex enough to need more people than astronaughts and so most people designing spaceships will never have the opportunity to use one.