As a digital designer you are a creator, and to create you need to master various skills. If you only master photoshop, I would never pick you for our product team. Photoshop just don’t cut it (I’m actually considering to uninstall it, to prove my point). Yeah photoshop is great for advanced compositions and photo editing, but far from essential in webdesign productions.
I don’t agree with this quote from @Folletto:
So: you don’t have to learn a bit more outside your discipline, but you could.
Based on this well written article
Being a jack of all trades makes you a better digital designer
You need to master a basic set of skills to make your (or your boss) ideas & design come true. This skillset can vary, but all great digital designers I’ve ever listen too/worked with/admired they got it. They got the aura of jack of all trades, and still master some handpick skills.