Lens top position is not one I consider a problem even to PSG, even as PSG is jot exactly at the top they will possibly get to the top and win the trophy, I would wish Lens will win and have a different record for the league again after a long stretch of PSG serially winning the title, so we get to see the variety in the league.
I also fully agree with you, the fact of having PSG on a diet is already a problem for them, it's clear that these guys can do very well and they know they can do it in the shortest possible time, if they hadn't had a team like PSG against them they would surely have been able to think about winning the championship
Lens occupying the first position in the French League I personally think is some sort of placeholder agreement between the two club

Just kidding though but on a serious note, I don't expect Lens to fight till the end of the season and I don't even expect any other team in the French League to win the league title ahead of reigning champions Paris Saint Germaine.
After the Christmas/New Year break, Paris Saint Germaine are coming out smoking fire and I expect them to regain the top spot position from Lens.