This is sorta how our team does things, and so far it hasn't presented issues. Each service has the vast majority of its real logic in a single file. Worst case, one day this stops working, and someone takes 10 minutes to split things into a separate file.

On the other side, I've seen people spend hours preemptively deciding on a file structure. It often stops making sense a month later, and every code review has a back and forth argument about what to name a new file.