Let's be honest here. An item is exactly what it sounds like...an item. And an item is useless unless you have someone who can abuse it. Think of an item like a sword. A sword is a very powerful weapon, but if no one knows how to wield it it's completely useless. So, instead of complaining about all the "OP items" in the game, let's address the real problem here (the champions abusing them).
magic pole2 votes
with 
is op
are you telling me kale without relay is op?
Cloud2731 votes[{quoted}](name=magic pole,realm=NA,application-id=3ErqAdtq,discussion-id=9Ml2LVNE,comment-id=0000,timestamp=2016-10-13T18:51:47.857+0000)
are you telling me kale without relay is op?
Yes. An item doesn't make a champion op. An item is meant to augment a champion's playstyle. In this case, Kayle is purchasing it because her 'e' allows her to use on hit affects, which syngergizes incredibly with with a long range aoe ability.
Weathered2 votesUsually an item is considered too powerful when a variety of champs abuse it badly or a single champ abused it SO badly that it was a major problem.
EcchiOtakuTM2 votesNope, there are a lot of cases where an item just simply breaks multiple champs due to being too strong.
If it's a champion abusing an item then that item wouldn't be as strong on other champions(such as kog who attacks 2x faster than anyone else with rageblade+on-hit items)
While if an item is just constantly and consistently strong on a wide cast of champs it's the item that's overbearingly strong. For example cinderhulk tank meta, or when tank items scaled off HP, and there's still other cases like the most recent being rylia.
However I just fear when riot tries balancing and end up with sejuani'd nerfs when they nerf champs who use the item then finnally nerf the said item.
1011001110001 votes
Champions abusing it: 
Literally every mage is using it. There are almost no exceptions. Are we really gonna nerf an entire class of champions because of a single item being bullshit?
D3M4L1S1 votesDOn't forget mord.
Astôlfo1 votesBecause items can be abused in a broken way?