I don't think he has been that bad compared to expectation
I think the problem is human nature.
Most fans went into this season expecting to move on - be challenging convincingly for the top four again, maybe go one better. Barkley to morph from 6-7 goals and impressive play into the world beating midfielder we've all been expecting.
Having gotten used to doing well pretty much all the time, and even when not doing that great, conceding few, fans now find themselves in uncertain territory. Human nature when faced with the unknown is often to panic. Of course no rational person panics, so instead their mind searches for 'reasons'. How rational those reasons are is down to how good a person is at controlling their initial feelings and thinking through an issue. Many people convince themselves they do this, but get locked onto an idea or a reaction before logic kicks in, and find it very hard to let go.
Road rage is a good example of this. Ever have those moments when someone else's driving causes you to let you expletives, gestures, threats? That's a reaction, not a logical conclusion. But most people in that situation will then keep repeating the faults of the other driver, to convince themselves their reaction is justified, instead of thinking 'who is all this vitriol helping?' and realising the anger, is all theirs.
So the expectation.. team isn't fulfilling. Sitting there in the cold thinking 'all this time and money invested and where the fuck is last years team?!'. Then Barkley gets the ball. Good old Ross, the little superstar. He can make something happen! Yes.. oh. FFS!
Easy to understand why the reactions. What people say after that moment of frustration? That separates the rational fans from the reactive ones.
I guess the only thing that is surprising is that quite a few fans seem surprised that a lot of fans post emotional reactive posts instead of logical ones. We aren't logical creatures by nature, and there is absolutely nothing logical about our love for our club, or our love of watching 22 overpaid blokes kick a leather ball around an oversized back garden (well when the right 11 of them are doing it successfully anyway).
It is annoying when others hold to different opinions, but if everyone thought the same then it would be pretty boring, yes?