This is a good question — I’m a technical-leaning designer so I’m partial to just using browser-based tools. I think things like Deco and Expo Snack are wonderful.
That said, I’m specifically looking at improving the efficiency of designers’ workflows without changing them. My team is part of DesignOps at Airbnb, maybe useful to consider it analogously to DevOps. ~= “We’re changing the servers that our applications are deployed on without forcing our engineers to learn a new language”.
Anyway, 1) having Sketch templates always-in-sync with real components is huge, 2) we’re building custom UIs on top of Sketch to use those components (which we may open source eventually), 3) this is a baby step to get us to the point where component-centric tools like Deco and Subform are good enough to realistically switch our design team to.
In theory a full design system has most individual pieces defined. You know what your button styles, inputs, headers, etc are and designing new layouts is often a matter of rearranging these various components — you'll occasionally need to design new ones, so that's the outlier here.
This ensures designers are using a single source of truth when it comes to existing components (which is pretty spectacular, because traditionally designers often maintain an overlapping library of static components for design purposes). It also helps hugely that I could pull in real data instead of trying to transpose some real-ish information into a static mock-up.
And of course there's still that design/developer grey area. I'm educated as a designer, but I'm extensively knowledgable about HTML/CSS/SASS — and that still only takes me so far. I know basic JS, but I'm not going to pretend that I can use React. Sometimes I still need to build static mock-ups so I can try out animations or storyboard userflows, do usertesting, etc.