"They don't realize that, in addition to engineering, I actually..."
(1) If they don't realize those things, then you've written your resume and cover letter all wrong, and you're selling yourself in interviews all wrong. Even if you spent most of your time writing code, de-emphasize that aspect of your accomplishments and sell the other aspects.
(2) Perhaps you're talking to the wrong "They", i.e. you're applying for the wrong jobs.
(3) If you're looking to work for a company larger than your startup (which is likely), then think about the parts of your work at the startup that you enjoyed the most and want to do more of. In larger companies, people tend to have roles that are more specialized instead of being jack-of-all-trades. Pursue opportunities and market yourself around the specialty you want to do more of. Tell people "I enjoyed doing X and was successful at it, and I really want to develop my skills in that area."
(1) If they don't realize those things, then you've written your resume and cover letter all wrong, and you're selling yourself in interviews all wrong. Even if you spent most of your time writing code, de-emphasize that aspect of your accomplishments and sell the other aspects.
(2) Perhaps you're talking to the wrong "They", i.e. you're applying for the wrong jobs.
(3) If you're looking to work for a company larger than your startup (which is likely), then think about the parts of your work at the startup that you enjoyed the most and want to do more of. In larger companies, people tend to have roles that are more specialized instead of being jack-of-all-trades. Pursue opportunities and market yourself around the specialty you want to do more of. Tell people "I enjoyed doing X and was successful at it, and I really want to develop my skills in that area."