A five-point lead is not very safe, especially with the season only having completed half the matches so there are still surprising things that might happen but it's true what you said in Ligue 1 if PSG is already in the lead then it will be difficult for any team to bring them down from the top of the standings because they have more strength than any team in Ligue 1, what can make them fall is when they lose concentration or when they have to divide their focus with other tournaments that are no less important such as the Champions League.
There are four matches in Ligue 1 that they have to play before facing Real Sociedad, and these four matches are quite tough in my opinion, especially when a few days before competing in the Champions League they will face Lillie because in the last two meetings, Lillie was quite troublesome for PSG even though PSG managed to win and draw but they will never take this match easily.
In the Champions League, their journey will never be easy, especially achieving what the club owner hopes for.
PSG on secure top standings position in Ligue 1 because they have 5 points remaining from Nice and seems difficult catch with PSG points, not really difficult for PSG keep their dominance in Ligue 1 although have inconsistent performance but the rival teams performance still not compete yet and they losses many points and failed close their points with PSG. Ligue 1 matches will begin on next months or get postponed more than three weeks later and PSG have getting many days how to get rest before facing Lens on next months.
PSG must improving their performance in Champion League, almost eliminated from group stage although last match get crucial points against Dortmund and success qualify to 16 of round. In Champion League match, PSG will face not really strong team Real Sociedad and seems they will be easily for setting quarter final phase.
PSG will continue to appear consistently in League 1 because no other team can replace PSG at the top. Moreover, Nice is not that consistent so PSG is not too worried because PSG will be able to prepare for matches in League 1 and in the Champions League maturely. Luis Enrique has experience in facing a situation like this and what is certain is that PSG will not feel pressured by the large schedule because in the previous season PSG felt the same way and in the end PSG was still able to win the title in League 1.
Yes, PSG's more important focus is the Champions League, although the domestic league is also important for PSG, but PSG is used to fighting rivals in League 1, so PSG can still handle it well and I think the match before the Champions League match PSG will have to face Lens, Brest, Stasbourg, and Lille, this is quite a tough match, but I'm sure these 3 clubs won't be able to beat PSG easily.