You know, sometimes there's a reason that people don't do things. People stop playing Darius? It's usually because something happened to Darius that makes him less-game breaking. I get that all champions should be amazing and valid and carry you to victory like a shining steed because you're the one special snowflake, but why do you think so many people pick these "meta" champions? Usually, when the game gets balanced, some champions are marginally better than others. A lot of things on this list is either mechanics countering each other (you know, COUNTER-PLAY), or bad choices.
Of course you're going to lose to LB as Brand. Brand's signature ability is an AoE blast. You know, a skill shot. That you can dodge. LB's kit is centered around deception, and popping up all over the place. Ahri is designed to be agile, so it's hard to hit her with skill shots. That's why you force her to do these things before you try to kill, or use your skill shot to burn her dash/zhonia's/flash. Your argument with Malzahar? It's called balancing. I know some people think Riot is horrible at it, but they make these decisions for a reason. The only person in the game that can suppress someone and still move while doing it is Skarner, who can be a problem but is much less scary in a 1v1 than Malzahar or Warwick.
Some of this looks like user error more so than champions being weak. Fiora vs Riven is bad, because Riven has hard cc, a shield, a dash, a real big combo. She is beatable as Fiora, but you want to know what Fiora doesn't have that gives Riven an edge over her? Hard cc, a shield, an escape... Fiora is really hard to play successfully because you have to know what she does inside and out, and you have to know how to play every matchup backward, forward, upside-down and sideways. Why else do you think she's infamous for being caught out in higher level play? Darius can be a monster. Even if you build tanky, during the laning phase and during teamfights he can have some impact. There's a reason they gave him the "Dunk Master Darius" skin. His ult can dunk people pretty hard. Xin Zhao... I don't know what your problem with him is, whether it's bad mechanics on your part or bad decision making, you should be fine if you're a good Xin Zhao. He's got to be one of the most popular champions on this list. :/
