Oh, so you need to buy items or use Summoner Spells to do what Riven does on her own? What a surprise. Who would have thought that they could make a difference.
Annie has no range and is squishy as hell. Not to mention, when her 4 stacks are up, she can do nothing else except E without burning them.
Kennen's E is a Move Speed Buff, but not a significant one. It's primary purpose is to charge for W. He does need Flash and Protobelt to pull off something exciting, but Riven can use these too if she wanted to.
Brand's Q and W are both skillshots that can be easily avoided. His E is not, but it really helps his E to have the target already on fire, requiring Q or W to be fully effective. Brand's Ultimate is reduced to almost nothing if your teammates separate or he targets someone who flashes into a null zone (away from allies and minions)
MF's ult is pretty awesome but has a limited range. Once she uses it, she has little left to really scare you with.
Riven can bunny hop into your team while shielding and decimate everyone while gaining health from it, shielding from it, and doesn't require any of your fancy items to do it.
Apples and Oranges don't compare.