-if we actually had some strong HP itemization options.

Just sayin'.

Huh, i guess you are right. Imma go build 4 ruby crystals, then turn them into black cleavers for 1000 HP HUEHUEHUE

4 Black Cleavers = 1000 HP...there you go.

Don't forget the glorious new defensive tree. Turn that 1000 Health into 1040!

You'll be able to take 0.15 more hits from a BC champ before dying!

So any word on why they felt the need to add such a spastic armor pen item?

Ostensibly because Pantheon and Talon need to be stronger on Summoner's Rift.

They don't given the way penetration was swapped. That mechanic is a strong buff to lategame AD caster damage alone.