Design can be tough because there’s a lot of ambiguity. There’s ambiguity in the product development process and in your own career. For example, someone can aspire to design for Apple and dedicate an immense amount of time and effort into developing a portfolio to apply with, and turns out that Apple won’t hire them. Maybe it’s their portfolio, or their personality, or they just aren’t looking for another designer at that time or already had their eyes on someone else. There’s a lot of failures (aka learning opportunities!) along the way. It’s important to be flexible and have some broad goals.
Keeping things in perspective, having to deal with your weak spots are the least of your worries. If you have a goal, do whatever you gotta do to get there. Figure out how to work situations in your favor. Not everyone goes into industrial design because they want to market research all day, but it’s part of understanding who you’re designing for. They also don’t do it purely for the engineering, but collaborating with those that make your product function helps you maintain your design intent. Everyone’s a critic, and designers continuously have to defend their ideas every step of the way. This can be challenging, but it helps you be strategic about what ideas you proceed with and how they can be better.
Basically, don’t let insecurities hold you back and be scrappy before you make a big commitment. You have a marketing degree and some professional experience. Are there design communities and events near you? Meet with designers for a chat. Let them know what you’ve been up to, what got you interested in design, and how you can leverage your prior experience and resources to pivot into design. Most importantly, keep in touch!