For reference here are the upcoming changes for Pantheon:

Heartseeker Strike

• Base damage reduced to 80 / 130 / 180 / 230 / 280 from 80 / 140 / 200 / 260 / 320
• AD ratio reduced to 300% Bonus AD from 360% Bonus AD
• Damage against non-champions increased to 60% from 50%.
• Base damage increased to 48 / 78 / 108 / 138 / 168 from 40 / 70 / 100 / 130 / 160. AD ratio vs. non-champions unchanged.

Grand Skyfall

• Reduced cooldown upon cancelling increased to 30 seconds from 10.
• Mana cost reduced to 100 from 125.
• REMOVED: Mana refund if cancelled.

Let me start this by saying that Pantheon has the 4th highest winrate right now at 55.17% with a pickrate of 5.6%.

In my opinion Pantheon had the nerfs coming due to his high winrate, but I think they are nerfing him the wrong way. Pantheon has always been that champion that falls off hard late game. These nerfs will make his late game even more hard. A slight power shift would have been best for him. Nerf his mid game damage and don't change his late game.

Also the nerfs to his ultimate are kinda hard on him. No mana refund if it's cancelled and the timer goes up to 30 seconds until it's ready to be used again instead of 10. Pantheon's ult is a great ganking tool for him. The cooldown on it is fairly high (150 / 135 / 120). The channeling time of the ult is long enough for many variables to change during the fight and at times you must cancel it. This will blow 100 mana and given Pantheon's small mana pool, you will go near OOM once you used it again to land on someone and use a full combo, rendering you useless for the rest of the team fight.