Why make champions so easy to play?

As a player, I ended the preseason at plat 4, so you'd expect the overall skill level of players to change, right?

WRONG

Almost every single game I play, whether it be a win or a loss, the 1 champion that always gets fed and carries the enemy team are the champions that have next to 0 skill requirement. To all you lower ranks out there, even at a Platinum level champs such as Yi and Annie are the champions that carry games. Truthfully, I think that while it's important to have champions that are easy to pick up for newer players, it's extremely frustrating when they're able to dominate so hard at a higher level. Most every single game I play with an enemy who picks one of those champions, they get extremely fed and win. I know someone will make some sort of comment about how teams suck and all, but in both games where I play against them in lane and my teammates, they always lose. Honestly, at the moment, there's literally no tradeoff between picking a champion that's easy to play and can carry vs a champion that's hard to play and can carry. After all, why pick a champion with an incredibly harder kit to use effectively, when you can pick a champion like Yi or Annie and get the same results?