I think the problem with Kev is not down to him at all, it is down to the team, ala Fellaini.
Personally i loved fellaini, great player and didn't want to see him go. McCarthy was signed to replace him and you can see why, he fits into the team better and plays the role more. Which, is also applicable to Kev...
Mirallas is a selfish sort of player, the type who will look for goal when he can do, and often focus on that rather than being aware of the team mates positioning. Before, this was not an issue for us, he scored some great goals and was a key player in the team. Now he doesn't fit the mould, as the team is now building chemistry among themselves and linking up with each other. Rom/Kone/Del are all creating, Barkley is playing off their backs (hence the goals he seems to nab) and the system for the most part, works. Add kev into that and you remove a 'team' player, and add someone who may not look for the pass to the striker, or someone who loks to be the hero.
You can forgive Del for messing about because you know he is creating now, not just going for goal, but Kev sadly not in the same vein anymore. I'm not slagging Mirallas off, far from it, i rate him as a player and any other time would be first choice on the left, but i'd rather have a link up player in kone than a direct wingerr who likes to wander to the middle right now.
Perhaps mirallas saving grace could be the kone role if he picks up a knock?