I have spent my working life so far as a generalist. I know a little about a lot of things, master of none. This is not conducive to a driven and purposeful career.
How do you create something essential when you are not a subject matter expert? How do you become essential to a project if you are not the central producer? I see a couple of options.
You can learn. Become a specialist with dedication. Never in the history of the world have we had so many learning resources at our fingertips. You do need the time to dedicate to learning. This gets harder with things like family and children tugging at your attention. Practice makes perfect though, So plugging away at something will make you better, and therefore more marketable.
You can become a coordinator of experts. Imagine a goal and assign roles for those with the expertise to cooperate and create something bigger than the sum of its parts. This is what I have seen in business. The energy to talk and link people with each other is priceless. Having a role in mind for all the experts and relentlessly networking, calling, meeting, discussing with them the best way to achieve that goal. This leads to success.