It's easy to be vector when you throw away the pixels and work in points. I've used illustrator for 10+ years every single day. Sketch is way, way faster to get work done. I generally don't draw 600 circles on a screen. I do however curse the heavens trying to work with layered art that needs to include bitmaps in illustrator. I use illustrator when I need to create a vector icon to import into sketch.

Sketch has a much better workflow for designing apps. I used to use illustrator. Speed of rending objects is important, but even if objects rendered 500x slower on sketch I still get my design done 10000x faster in Sketch because Illustrator doesn't support the workflow.

I have no problems using UI8's WireframeKit Sketch files. It has a bunch of vectors and artboards as you can see below.

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