As in reduce crit damage by 45% making crit builds less then ideal and in turn making marksmen have to "build more AD" to counter this item.
It would work just like % armor penetration in making a large part of a stat effectively worthless.
AHarmlessTaco2 votesSee: Randuin's Omen
Irelia Bot1 votesthat is only 10%
Cat cafe1 votes
Irelia Bot1 votesThe lack of % armor pen in that build is laughable.
Or are you trying to say that diversifying marksmen builds becasie of real counters to some aspects might actually make their builds more dynamic then just which zeal item do I build?
oSEXYPLATYPUSo1 votes
should only be built vs 2 or more auto attacked based champs
and never built as the only armor item
it needs to be paired with anything that has armor and hp but ideally something that has debuffs
for examples
Irelia Bot1 votesFor some reason feel like people are not getting that i am saying Last Whisper and the items it builds into make high armor builds a joke.
oSEXYPLATYPUSo1 votesbut 45 % reduction is flat out broken and op
Irelia Bot1 votesThen why is taking 200 bonus armor and removing 90 of it not OP? They had to invites at least 2 items into getting that armor and then 90 armor (1800 gold worth of stats) suddenly becomes worthless.
oSEXYPLATYPUSo1 votesok lets use 
for example... he has 99 base armor at lvl 18 and if he gets 200 armor in game from runes/ masteries/items he has 300 armor and if they reduce his bonus armor by 45%
he has 99 armor + 110 armor for a total of 210 armor left