“Headless” is very marketable, but “head” is not the best metaphor for an interface. People don’t have more than one head, and their head never changes. A better but less catchy metaphor is a hat. Like hats, your interfaces change to meet the user’s situation.
We have done monolith implementations, and we have done composable implementations. Any major commerce project has challenges. We believe the notoriety around composable's complexity isn't because it is harder than monoliths but because it is different.