I'm really curious about this question, are you thinking that not having Scrum makes it's harder to refine features?
I'm trying to understand what assumptions you are making, because I've never worked in a Scrum environment, but have always refined features as part of the natural flow.
"natural" as in "law of nature"? Or is it just a process which crystallized in the course of your career as something which makes sense to do?
Scrum, and other methodologies are mostly a collection of such processes which proved to be useful, are somewhat standardized for learning and communication.
One can reinvent many of the Scrum processes independently, but I kinda don't see the point. Just like I'd rather use a finished library / framework rather than try to hack together my own.
The answer might be simple for small teams, but a lot more complex for larger teams, where the result might look eerily close to Scrum. One difference would be that meetings will take place infrequently and only "as needed", where I wouldn't trust most teams to recognize their needs.