I think Sketch is not meant for icon design... you're right, the pen tool is a nightmare to use, but that's because they are not trying to replace Illustrator for icon design work. I recommend doing vector illustration in the program made for vector illustration, and UI design work in the program made for UI design.
Don't agree. I do EVERYTHING in Sketch, and most of the times it works pretty well. Of course there are limitations, but apart from that Sketch is a very universal and capable tool for every design challenge.
I think Sketch is not meant for icon design... you're right, the pen tool is a nightmare to use, but that's because they are not trying to replace Illustrator for icon design work. I recommend doing vector illustration in the program made for vector illustration, and UI design work in the program made for UI design.