Firstly, PSG's defense is not in a good position now. Secondly, I am not happy with the performance of their goalkeeper Navas. I saw two goals from Brest in yesterday’s match. If the goalkeeper had been a little more aware, opponent would not have scored from these shots. Hopefully Ramos and Donnarumma will improve their overall situation.
PSG defenders are never at top level. They can play well in Ligue I but in Champions League, they bring uncertainty when opponents are top clubs. It is abnormal to see PSG conceded many goals from French clubs. You are right that Donnarumma and Ramos will help them when they are in the squad.
For the second game in a row, Psg conceded two goals from not very strong teams. Offensively, everything is in order, even in the absence of Messi and Neymar. But the defense is not yet in good condition. Perhaps Ramos will change the situation for the better. Pochettino will have to work hard to create a balance in the team, otherwise, in games with stronger teams, PSG will be severely disappointed.
With Donnarumma, Ramos, Messi and Neymar in the future matches, they will be unbeatable in both defense and attacking systems.
It is not easy to beat Donnarumma and with support from Ramos, Marquinhos will improve his defensive leadership. Messi will bring more key passes and goals for PSG.