Yes, he has weaknesses - most notably his mentality, which is a huge stumbling block. And I don't think the matches are always on his racquet, just more so than Milos. I have seen Kyrgios reach a higher level than Milos - one that can challenge the Big Four. Milos doesn't have that higher level; when he's at his best, he can beat one of the Big Four, but only if they aren't playing their best.
Again, it is a floor/ceiling thing. Milos has a much higher floor than Nick - he doesn't give up on matches, doesn't disappear, just looks wooden and one-dimensional. But I've never seen him play a truly elite game, whereas Nick at his best is simply explosive and truly elite.