This is all hard to do IMO if there's one running backlog.
The benefits of sprints I see is they're a useful time container for planning purposes. Eg:
- we can allocate larger pieces of work to upcoming sprints. This is done very loosely just to get some idea of what we can take on, and when
- we can allocate a fraction of each sprint to tech debt or platform improvements etc
- set a goal for each sprint which is some observable step forward. This has taken practice to break down the work into appropriate chunks which can be verified done
- record velocity across sprints just so we have a rough idea of what we can get done in a sprint (it will vary of course)
Yes, there is overhead from the planning meetings. But this helps all of us get involved with incoming work, which I think is better than tasks coming from nowhere without context.
I think the right methodology depends on the context of the business. If product teams need to work together towards something, or if there are competing project priorities, then sprints can help protect focus and provide finer structure than just "Q4".