So...how do I win a match again?

well you have to remember: everyone else suffers from the same changes except lee sin, kindred and rexai players because they still do the same thing as before but better. but EVERYONE ELSE! has to adapt the same way, so if you ban lee sin and kindred in most of your games where you can ban and cry for lee sin ban every time you cant ban, you eliminate the only players who have an edge over you.

everyone else felt the same way as you, they simply didnt cry so much about it and learned how to play the new season. i cried too for two weeks until i got myself to learn the new stuff. i dont know what roles and champions you play and what runes and masteries you use, but you gotta experiment alot and maybe learn new things.

also it might feel like your old champions suck now but you can find ways to make them work with new setups and playstyles. at least it worked for me.