Symbols aren't as powerful as they are in Sketch. You can't do overrides, nested symbols, etc. The vector drawing tools are not as powerful. Even just selecting multiple elements in different groups are not as convenient as they are in Sketch.
The whole supposed advantage of XD is that you can do everything in one platform: design, prototype, and create design specs. But each of those respective tools aren't as good as the alternatives out there, so we find ourselves using Proto.io, and Zeplin anyways, negating any potential advantage to using XD.