I don't know why every positive comment about Naismith has to come with a qualifier. He is a good footballer, full stop. He won more headers last night than Barkley has won in his career, tracked back in defense, moved well around the box (though he suffers from the same lack of creativity that seems to be plaguing our entire team in the final third), and transitioned well when we won possession in our own half (the great hold up and pass to find Barkley for Lukaku's shot on the break stands out for me). No he doesn't go on mazey dribbles like Barkley, but he plays simple passes to players in good positions without giving away possession, which I strongly prefer. Barkley had a good game yesterday, but for me Naismith was my man of the match.
I'm not sure why even when Naismith puts in solid, all around performances, people are quick to drop him from their theoretical lineups. I would say it's because he's not scoring as much now, but even when he was scoring no one thought much of him. He scores at fairly the same rate against poor opposition and top teams, yet people keep trying to determine special circumstances where he's useful (with the implication being that he's not useful outside of those circumstances).
I know it seems strange, watching him it often doesn't feel like he's playing well, but then you focus on him for a period of time and he'll do a lot of things right and almost nothing wrong. But he's given far less reason to be dropped than just about anyone else on the team, with the only reason I've really seen being that Barkley is probably "better" and should therefore play over him.