if you really break it apart, it gets hairy.
you're ascribing virtue to "rule adherence" and then concluding an atheist (not sure what that means) has less rules to adhere to.
i think it loses weight on moral arguments. take stealing.
for a theist:
god makes a rule against stealing. god promises a reward for adherence. the theist abides by that rule.
for an atheist:
make a moral choice to steal or not.
both would be subject to social contracts, laws, etc so its a wash.
personally, i don't see there being much virtue at all, in obeying a divine ruleset that promises rewards compared to someone that simply makes a moral judgement.
outside of a moral argument, you can argue that a practising muslim requires a lot of discipline to pray / abide by the many rules. having said that, there are many religious people that have no discipline and don't practice at a consistent level. again we're ascribing a lot of virtue to the idea of discipline, but if a muslim that abides by many rules is obese for example...are we again giving him the "strength trophy" for discipline? point being: boiling down someone's "strength" or "weakness" based on religious beliefs or lack thereof seems too myopic.