I think there's a figure mostly absent in these processes. Designers and devs are living in their bubble/silo and don't think like a user.
It's very rare to find someone who can understand design, UX, and code and put it all together into a cohesive vision. In my experience, if you have the UX right from the start, then the rest becomes much easier. UX is the foundation that will dictate how it has to be designed and programmed.
But also in so many cases it needs to be made to work in reverse :\
Even when the pure logic or core process is where the real magic happens, and makes the app what it is, if interfacing with a user is very important you could also say that the UI is the actual heart of the program instead, which ends up calling that wonderfully unique code that may be different than anything else. Or anything else that has ever had a UI before.
But you need a "more common" interface that can accommodate optimized workflows of some kind or another, in enough ways for target mainstream users to make the most of the unique parts of the core creatively-engineered code, enjoying the most easily gained familiarity at the same time. With at least as usable a UI as they are accustomed to if not better.
Once that's all said & done is when I think it would be best for the creative artists to bring it up to meet visual objectives, with carefully crafted content curation, and run that by all kinds of ergonomic testers.
If they come up with any engineering shortcomings I would listen to them, even if it's nothing like an actual deficiency or true defect. There should be some pretty tight functioning and I think that would happen less often.
> if interfacing with a user is very important you could also say that the UI is the actual heart of the program instead
If it's meant to be used by humans, then yes. The experience should be the north star.
That doesn't mean that you have to sacrifice everything in favor of this. Obviously you need someone with enough technical knowledge to understand how to balance all the priorities.
Edit:
And by experience I don't only mean the UI per se. Also the performance of the whole system etc.
It's very rare to find someone who can understand design, UX, and code and put it all together into a cohesive vision. In my experience, if you have the UX right from the start, then the rest becomes much easier. UX is the foundation that will dictate how it has to be designed and programmed.