Shyvana doesn't "abuse" on-hit items. She uses them. She is built to scale with them. She is an on hit champion.
ADCs don't abuse crit items, they use them, they are designed to function on them.
Darius doesn't abuse BC, he is designed to build it, he is designed to use it.
Assassins aren't "abusing" lethality items. The items are just too strong. Assassins are intended to use them.
Abuse cases are things like Tank Ekko when he abuses his kit in combination with certain items to make a toxic gameplay pattern. Abuse cases are the current issues with Lethality + BC on Miss Fortune. They were not intended and create gameplay and balance problems.
Stop throwing "abuse" in your post as a way to make it seem worse. That is just like the people who say "free" a lot. "Ashe gets free permaslows", on no, trust me, she pays for it in her power budgeting.
Stop using word abuse to make your posts look cooler and your arguments "stronger". It doesn't work on anybody with a brain.