If he didn't operate just in the oppo's half (which isn't entirely true though, plenty of times when we switch to 4231 you can see him behind behind the #10 every now and then), people would be complaining that he's dropping too deep like they did when Rooney played #9 and he was constantly in midfield, nowhere to be seen near the box. Unless he possess bilocation abilities, you can't have it all, even more so when speed is, indeed, not one of Ibra's traits.
You say that being involved yesterday wasn't enough but the perception would've changed had we won. The chance he created for Pogba was exactly the type of involvement I'm talking about and not many strikers would pull out, it was down to Pogba's ineptitude that Ibra didn't have an assist there.
As for the left side, you're right, but at the same time you probably can agree that the left side is more flexible/capable of pulling out some combination play due to Pogba playing there, even when Mkhi's playing on the right wing you'll see him drift inwards towards the #10 position when Ibra is either in the box or drifts to the left. Valencia then has all the place on the right, and he needs it if we're to get the most out of him as an attacking fullback.