When companies are small the jobs are all blends because they have to be, you just don't have the resources to do more. But as the company gets bigger (presumably through growth and not just a funding bump :-) you can allow folks to focus full time on specific roles which, in theory, gets you better execution of those roles.
A friend of mine once said you often could figure out what role you liked "best" by the first thing you did when you got in, did you check the build? (developer) did you check email? (manager) did you check the web? (marketer) A bit simplistic but it does make for interesting introspection.
As employee #2 you're well connected with the CEO and the other founders, and you can talk about what you want in your future. You should sit down and have that talk with them.