We use Figma at work, and while it’s a nice tool I think it’s easy to fall (or maybe we just fell) into a kind of uncanny valley. The designs we get are close to realistic mockups of our actual UI, but are often not 100% there, and it’s the little deviations that can be quite distracting. Engineer: So are we changing the nav icons as part of this story, too? Designer: Oh, no, ignore that. I didn’t have our real icon…
Have a plugin which could turn the unfinished modal for example into a wireframe look & feel and then when you have the right icon, turn it off again.
I remember back in the days Expression Blend had some functionality to apply sketchy lines style (based on Bill Buxton's book - Sketching User Experiences).
Also, the prototyping functionality is still rather basic. Axure is much more powerful and ideal for the early sketching and testing phase.
But I'm sure Figma will have more sophisticated prototyping features in the future.