Both teams are close to each other and Marseille got only one point more than Lens however Marseille started the season better than Lens if I'm not wrong they had collected more points at the beginning of this season, While PSG is far from them I think the main competition in the French league in between Marseille and Lens for second place of the table.
PSG has secured its position at the top of the standings and could have confirmed the championship earlier this season in Ligue1. Meanwhile, another more interesting rivalry is true as you said where it happened between Marseille and Lens because the points of the two of them are very close and will change positions when the results of the next game differ. I think this is also quite interesting because second place is an absolute place for a team to directly qualify for the Champions League next season.