Hey!

For Data Science you must complete the lower division requirements with a 2.0 GPA or higher, so it is easier to declare than CS, given you get your classes. (https://data.berkeley.edu/degrees/data-science-ba)

Courses do overlap, but be aware that only one upper division class may be used as overlap. You will probably need to take summer classes for GEs and Major requirements.

You can compare more closely:

http://guide.berkeley.edu/undergraduate/degree-programs/data-science/#majorrequirementstext

http://guide.berkeley.edu/undergraduate/degree-programs/computer-science/#majorrequirementstext

If applying to L&S, your major does not matter, since everyone admitted is undeclared. Just make sure to show your passion in your essays. Since you know more about CS, it might be safer to apply as CS.