After starting items grab Chain Vest for 700 Gold as your FIRST item with boots. So 1050 gold and you can dodge his ult+reduce his DMG down to a manageable level.

It is almost funny.

Now once he has tons of Arm pen if he does LW, Brutalizer, Cleaver etc then adjust accordingly but this helps you weather the storm and he becomes a useless stun bot.

I like to catch his spear with my teeth, instead, but chain vests are also a good counter.

Or get cleanse

Or. Don't surrender at 25, laugh as their team has no kills because pantheon took them all and kill everybody. Hahaha, pantheon 26, team 0.

I like to tell my team to just wait at the fountain until 20 minutes have passed, then we go out and brave the storm since Pantheon had no kills for the first 20 minutes of the game and is unfed.

All you suggestions are typical.

Buy a chain vest and skip all your waiting BS. EVERYONE should have one, even teemo.

No need for cleanse when HSS does very little DMG when you have some ARMOR.

As I gather it from other info I have read from the Riot dev team HSS does not get a boost from armor pen, so a Chain Vest is adequate even as Pantheon purchases Last Whisper, Brutalizer, etc.