Most Underused Items - How to go about Improving?

I'd like to know everyone's thoughts on underused items.

Why? I was looking at the past removed items and recognized the "Ionic Spark". Back then, I wasn't even level 30 so I didn't think much of it. When looking into the item, it looked like the item I myself wished there was. Why? For kinda tanks that lack damage and don't synergies well with other items.

Shen is a good example. Pretty useless damage build. Pretty useless full tank. Ionic spark put him in the borderline. Now there isn't much favorable items for champions like Shen. There's triforce for burst and BotRK for sustained damage...but it doesn't give you necessary tankiness (and triforce gave mana).

Then i'm like, "Why did that item get removed?" After a bit of research, I discovered it just wasn't used enough. I started looking into other items such as "banner of command". This is a really good item. Good defense and offensive capabilities. What made it shine is its great map pressure (I actually win games because of this items active). I don't get it (except Ohmwrecker which genuinely sucks).

Some of these items in my opinion are underrated. Thoughts on underused items, how to make them better, and why they aren't seen is what this thread is for. Please reply.