I get what Xalara is saying, it's something I've wondered about alot.
When I started playing, it was season 1 and there was maybe.. 50 champions? I'm not sure, but it seemed like a bunch and I was seeing new champs all the time. Even having played Dota and knowing it'd take awhile to learn, it seemed like a pretty big task at first. I'd face a new champion, get wrecked by them, and think they were OP until I actually got to play as them.
I can't imagine how much worse it is now that there is so many more champs, and how much worse it'll be in another year, or two. It'll become a huge barrier to entry for a lot of casual players down the line.
The champion reworks rather then releasing new champs is a good start. I think they eventually need to slow down even more on releasing new champs, and doing a rework of the least played champion every month.