On one hand, I agree that his ultimate feels like it takes a very long time to land and is often feels like a liability to use to engage with, because his opponents have so much time to react.
On the other hand, Pantheon currently has a very high winrate, likely already deserving nerfs, and is an extremely powerful laning bully who can't afford buffs to his kit without nerfs in other areas. If his ultimate is improved, then he must lose power somewhere else to keep him in a balanced state. Changing his ult speed + zone to resemble Galio's would probably be an overall buff. Taking power out of another part of his kit in exchange will probably make him less of a lane bully, which will change his playstyle and niche. That might be a healthy improvement, or it might not be. More details are needed since your suggestion can't be implemented without an additional change. What power do you think he should give up in exchange for a smoother ultimate?