True, but historically riot has never has stuff worked out by the end of preseason. Whether its new dragons being slightly off -> cloud soul change, or changes that make champions too strong e.g the year Leblanc+a few others needed a nerf all the way through feb(cant remember year sorry).
This is potentially the biggest change the game has ever seen that affects balance, and while the balance team have been improving a lot, I would be very impressed if they had it even close to balanced by S11. I would expect more of an akali treatment where items are being tweaked and mechanics removed throughout the year.
We'll definitely be tweaking stuff throughout the year, but i do think we'll be able to get the game to a decent state pretty quickly.
One of the problems with trying to instantly solve balance like this is actually that it just takes time for players to adapt. We might see Akali is at a 39% winrate but secretly she has a sleeper op build that nobody knows at a 52% winrate. It's gonna take a lot of learning from both sides here