in most patches most of the champion changes are nerfs, i personally think this is the wrong way to go.

There a decent amount of champions that should be buffed for example i dont understand why corki nerfed after never being looked at for ages, you say he needed a nerf because hes the best ranged carry (damage wise) why not buff tristana or miss fortune a little so there on par with corki ?

People will always complain about champ x is op but champ x becomes op because champ y who was better then champ x last week got nerfed.

Tristana needs a buff? Are you high?

The problem with buffs is that they impact ranked play more and then the high ELO people cry and Riot has to tend to that champion sooner than they might want to.

At higher ELO, if a champ gets overnerfed it simply stops being played and is replaced by another champ in teams and they mostly keep happily gaming until Riot gets around to fixing it. If a champ gets overbuffed though, it will become op and keep being picked/banned, it will ruin games or take up a ban slot that could have been used on another champ, the high ELO players, who are fairly vocal, keep openly complaining about it and then Riot is more or less forced to react quickly to prevent further damage to ranked play.

TLDR: Nerfs don't damage ranked play, buffs can.

Riot thinks that overall the power of the champions being nerfed is above what they want the power level to be. Champions being OP is also more noticeable than champs being UP.