He missed because he couldn't fully control the output of his armament haki which has Top Tier potential and also because Kaido dodged after being told by Big Mom to guess what? Yes, dodge. And well, him being the second coming of Jesus is not precisely breaking news. He always has been, actually.
And btw, this biased guy is a Moderator. Let that sink in...
Also, is he overrated? Nah, he is rated just fine.