OFF: Why is this downvoted? It's a reasonable discussion regarding particularities of the game.
On: I, for one, would continue playing. There must be a balance in the number of "complex kit champs" and "simple ones". Let's name a few "complex champs", I would say: Kalista, Draaaaven, Cassiopeia, Syndra. Some might say "what's so complex in these champs?" well it's my personal opinion, you're free to consider them easy. Let me name a few champs that I consider having "simple kits": Garen, Vladimir, Darius, Yi, Annie.
What the game would look like without the "complex" ones in my opinion? Dull, boring as you say. Lacking outplay possibilities. Rarely you see "amazink" clean plays with "easy" champs. I agree with you, the game would be boring and would feel like constraining, limited.
However, what the game would look like without the "easy" champs? Almost impossible for new players to learn the game. The learning curve would be so abrupt, they'd give up trying champs they struggle with. They need to have their options in champ select as well.
If some feel insecure playing with Vayne and Kai'Sa because those champs feel too risky, and prefer safer champs such as Ezreal, then they should be allowed to. This is why I feel like LOL, despite having over 150 champs, feels like lacking over half of its possibilities. Remember that LOL is not a game made ONLY for competitive, "pro" players. It should also suffice the casual players' needs. Not all of us are Fakers, Gosus, and Qtpies. Some of us are gold, like me, and I am so happy with my tier, I just don't wish to be higher since I am happy with what I am. I feel like this is where I like to be, I play my champions, some of them "complex", some of them "easy", and I am so happy with the game right now. I don't want to be diamond, to shine with "amazink" plays. And there are plentiful options for those who want that to do it. Some are bronzes, and they feel like the game is enough for them right there.
You say you like "complex" kits, and I appreciate you, you might be in the future the next streamer I watch to when I want to see amazing plays. If you feel like the game needs more of those champs, you should propose some ideas of your champs here! :D Remember that Rioters are also humans, they have their imagionation like you have yours. They need to take their time when creating a champ, to make sure it's balanced, not OP, not useless either, not a "straight counter to X", not a "straight countered by Y", and most importantly, unique. Sooo, my suggestion, speak out your mind! If you have ideas, write them down here!