Have you ever heard the phrase, "High risk, high reward."? If they're hard to play they should have a statistical advantage over an easy-to-play champion if they land the same number of abilities. That's just how it is.
Also, take another look at what the opening post says. Apparently Orianna's able to get people to burn flashes with her Q. I guess that's level 10 players? I have a hard time imagining even Bronze 5 players doing something that stupid. If the Orianna places the ball on a J4 who ults in, it makes sense that people would flash away, but even without boots pretty much any champion can just walk away enough to not get hit by ult if the Orianna doesn't position perfectly.
This is what goes on in every Zed main's mind:
"Let me throw my W over here.
What's that? they all dashed away? well, darn....
Okay, let me throw my Q at them.
What's that? They used their flashes? Why? All I did was Q!
Okay, let me dash to my W.
What's that? They don't have their flashes? Time to ult!
What's that? My ult, e and q do around 2000 damage to their ADC? That's insane! I don't even have 125 AD, yet!
Wow, how neat is that!"
See the hyperbole?
Orianna's Q, W, and ultimate, assuming they all land, deal 945 base damage with 200 AP at level 11. At level 6 with 100 AP, her combo does 530 base damage. Zed's base HP is 1459 at level 11, or 1059 at level 6. Zed's base MR at level 11 is 46, or 40 at level 6. That means he has 31.5% damage reduction from magic at level 11, or 28.5% at level 6.
Assuming Orianna has 8 magic pen in Runes (the standard), Sorcerer's Shoes, and the Precision mastery, she has a total of 27 magic penetration at level 11. This means that she'll do 84% damage to Zed, or 794 damage. This is assuming Zed's an utter idiot and builds 0 MR, which is highly unlikely. So, best-case scenario for level 11 Orianna, just over half Zed's health. 54.4%, to be exact.
Assuming Orianna has 8 magic pen in Runes (again, the standard) and the Precision mastery, she has a total of 11 magic penetration at level 6. This means she'll do 77.5% damage to Zed, or 411 damage. This is under half Zed's health. 38.8%.
If Zed is halfway competent, he won't die in lane against her. Not only does the full combo deal nowhere near the damage required to hit him, but he should also be evading Orianna's skillshots anyway. It should also be noted that Zed's standard rune page gives 12 MR, so Orianna doesn't even do that much damage to him.
If you die 1v1 in laning phase, you've done something wrong. You've made a mistake. It's not the game's fault.
This all to say, Orianna has no means of dealing over 1000 damage past MR with her full combo with under 200 AP, let alone if someone evades her Q. So, no, Orianna's not OP, by any stretch of the imagination. You just have to play smart. And yes, I know some people even in the LCS die solo to Orianna. They made mistakes too. If the champion was objectively overpowered, Riot would nerf her sooner rather than later. Counterplay is something they take into consideration, and Orianna has plenty.