I noticed some teams at fb have both ML software engineers and research scientists working together. What are the major differences btw. these two roles? For example in terms of type of work (RS focuses more on state-of-the-art papers, only building proof of concept prototypes without worrying about production, whereas SWE works more on actual product not fancy academic publications) and performance evaluation metrics (RS is evaluated by publications whereas SWE is evaluated on user metric gains). Are the lines more blurred than I think?
No difference. Research scientist title is held for those with doctorate degrees and prefer the title
Both are required too write code, which can be hard if you are on PHD side with less passion for code
RS is any PHD, you can be researcher or swe.