Yeah, here's the thing. Those ones you listed? They're not the most OP. They just somehow became meta picks.
I'll show you OP.

And I have barely even tried 1/8 of the champion pool so far.
Also
, as stated, is a well-known and overpicked OP along with
(tho 99% of people who pick them don't know how to build them).
Here's the other thing.
Items.
URF players are stupid, and their idea of "OP" is "I can't counter dis guy while building irrelevant glass cannon trash"
Here's a little gem for you:
.
Those annoying stealth champions? Yeah, this thing in URF gives you 10 seconds of true sight on a 15 second cooldown.
Enemy has no stealth?
. Yellow sucks on URF. You need to be mobile. Riot overbuffed this from last year, when it was already amazing. Now it can provide persistent vision for you on a tiny clairvoyance cooldown. Scout ahead for free, check all bushes from massive range. The only thing you miss out on is teleport targets, but you can carry a normal ward for when your teammates ask for one to go in on.
http://boards.na.leagueoflegends.com/en/c/GD/l3axGYl1-the-real-urf-ops I list a bunch more. Seriously guys, stop overpicking boring champs, and start using your brains for SIMPLE ways to actually win.