[c7h]

It sounds to me like it's not because of your skills and experience. You have been working in your field for a long time. Very few developers are "rock stars". We all build on the shoulders of giants - sticking code together is a pragmatic approach - especially if you work for a startup. But it sounds to me like you're comparing yourself too much to your ideal. My tip: Compare yourself less with "rockstars", learn the skills you are really interested in and reduce your working hours to a bearable level.