Pantheon's ult is messing with my brain

Why is his ult so hard to land and the biggest problem why does he insta cast the ult when you click somewhere outside the cast range instead of walking to an place where he can get in range so he can ult? And it seems hard to land it somehow, and of top all of this it has the same problem like galio's ult, it looks flashy and powerful but does it do something other than that?

https://imgur.com/a/TjQxtYO : Some explanation on what happened to me while using the ult