User blog comment:Aphostropils/Questions from a beginner/@comment-27233636-20160411011239

1) An item granting armour debuffs would be fairly over-powered in todays meta. Vayne's popularity and massive damage comes from her lack of care if the enemy builds armour. Today's meta is a armour/tank meta. 2) The meta evolves based on what items, champions, and such are good, while the items and champions and such are changed to be balanced within the meta, causing a strange, set-in-stone rule-set that changes when the meta loop is accidentally broken. I personally care little for the meta as it only allows for a specific set-up and forces itself into everything. 3) Some such classes could work, however, they are generally avoided because of the meta. However, while there are no true Tank Marksmen, Urgot and Graves are both Marksmen with quite tanky qualities. Unfortunately, because of the meta and it's lack of want for such a concept has kicked Graves to the jungle and Urgot... well... is the least popular champion atm, behind even Yorick. 4) It depends. You could never get rid of Tiamat from Riven or Rylai's from Aurelion, but less important items should be replaced if a different item would be better in a situation. Two damage items and then defenses tends to be best for everyone but full tanks and supports, however.

I'm actually newer than you, but I had an answer that I hope helps, so here you have mine.