It wouldn't break the game now, a few weeks after launch. One etheric light per week (per 2 weeks if you don't max both marks) seems like a reasonable way for players to progress if they don't or can't do the other options. However a lot of people went into the launch with full marks already. They would have been able to buy 6 etheric light immediately and reached the level cap on 2 characters before doing anything. That would have been absurd and is definitely not something Bungie would have allowed.