Personally I think rotating when they're playing well is the perfect time to do it, on several levels. It gets them used to playing with other players while they're playing well, it keeps the likes of Tomi match fit, less of a shock when we pick up injuries, keeps everyone on their toes and it also becomes less of a 'thing' to not be picked now and then.
It also keeps midweek teams a bit stronger. You could play Tomi and ESR in the league and rest Martinelli and White. Midweek you can then play all four in theory.
At the moment you can tell Arteta is still hesitant to disrupt a good thing, both within games with his subs and from the start. It's understandable because at the moment we still have it all to prove, but it's something we should be aiming to move towards.