The difference between data science and algorithm development
A data scientist has many general skills, such as

data collection
software developer
data engineering and cleansing
algorithm development, selection and refining **
statistical analysis
data visualization
etc.

A deep learning algorithm developer would be more specialized, concentrating more on that one aspect of the data science field, and less on the other skills.
Typically an algorithm developer will be part of a data science team, consisting of members having different skills, but overall the team will possess all of them.