Barkley wasn't great last night, but he is still a great player, playing in a difficult position and will get better at it as the years go by. He might also need a bit of help to be mentally stronger in the games, not letting the mistakes affect him and being able to refocus, difficult but I'm sure it could be worked on.
It's a lot of pressure being the main supplier to Lukaku. Mirallas was also really poor in the first half, giving the ball away a lot and drifting in too much, if Koeman had a decent enough replacement I think he would have gone off as well.
The second half saw our wingers played much wider which created space in the middle and the crosses hit their targets. I think Barkley would have benefitted with having Bolasie and Deulofeu either side of him.
I don't know why people are so keen to put him down, he seems a great lad, works hard and is a blue, personally I love watching him play.