It does 'water down' your design abilities over time.

Understanding how your designs work is one thing, that's a must. Coding it isn't. Spending 50% of your time implementing the engineering of your design is 50% less time you spend practising design and improving.

This stuff isn't like riding a bicycle. Especially around the visual side of design — try not drawing for a year, skills fade over time. You'll have to work hard juggling those plates, keeping up with your peers that are focused on either design or engineering. It can get exhausting.

But of course there's advantages, you can build stuff. That's empowering. You have a lot more options when freelancing.

This is something I'm trying to work out myself. For my clients my ability to design and code saves them money and time. Though when I work with front-end developers I notice how focused I am on the design compared to when I code it. That focus results in better design. I'm working on this, it's a challenge to make sure I don't get spread too thin, respecting my design and engineering process and making sure neither eat into each other.