My list of changes to key champions next season

Buffs:

Kennen - His Q hitbox is too tiny you need to increase it by 50% at least. Also his AP scaling should be increase by 20% because it sucks and I feel like I'm doing no damage.

Yasuo - His windwall needs to be increased in length and width by 40%, also it needs to stay up for 3 more seconds in my opinion. Also his dash cooldown is too high. Make it 0.25 seconds, not 0.5. Too much mobility in this meta and he is unable to keep up with things like Zed and Kha'Zix.

Jayce - Increase his AD scalings by 25% because he again feels weak especially in melee mode.

Quinn - Increase AD scalings by 25% again she feels weak due to her poor mobility.

Nerfs:

Kindred - Decrease her ultimate duration by 4 seconds. This BS is so broken, like really? Free invulnerability? That tilts me so hard. Also look into increasing the spawn timer on her marked mobs, she gets this ridiculous %HP physical damage buffs too quickly.

Vayne - %HP true damage is so broken, there are no ways to itemize around it so that needs to be removed. Compensate it with a buff to her tumble by reducing the cooldown by 10%.

Ziggs - Decrease the radius of the inner circle on his ult. This no skill AOE doesn't deserve to wipe an entire team. He is the king of poke but that is not an excuse for a penta from halfway across the map.

Mordekaiser - Remove Rylais entirely and Morde should be good to go. His synergy with this item is crazy. Remove it and suddenly he's not a problem anymore and you can focus on the 100 or so champions that are relevant.

Syndra - Reduce her AP scalings by 75% at least on her ult, so that it doesn't do tons of damage and isn't press R to win.

Hope you take these suggestions into consideration.