I don't fully agree. however, yes, because Galtier is the trainer. Of course, he contributed to PSG's elimination in the Champions League. because in fact, Galtier failed to bring PSG much better than previous coaches. even so, we can see PSG's failure from various factors. especially, after the post-world cup. the injury to the core players, made PSG's performance decrease. Likewise, when PSG played Bayern in the second leg of the Champions League.
He did not have enough experience in Champions League and PSG is a biggest club in his career. I am sure he would feel stressful and pressure on his shoulders in PSG. In reality he failed to help PSG players at their highest capability and failed to help them going far in Champions League. Failing in Champions League always is a big minus point for any coach in PSG.
I can't completely say Galtier's failure was purely, or should we say his fault. because IMO, Galtier is a pretty unique and intelligent trainer. unfortunately, the system he implemented on his team did not go according to what he wanted. I just want to say that PSG lacks a decent midfield player. be it an attacking midfielder, or a defensive midfielder. as a result, when PSG came up against a team on par with them. often, PSG's front line cannot play optimally.
It is not a pure responsibility from a single person like Galtier but it is a responsibility of a whole team. PSG players could not play well in many Champions League seasons, not only in this one. In the past ten years, it is barely to see they went to quarter final or farther than that. Messi and Ramos did not help them to win Champions League but their results are worse in the last two seasons.
They must rebuild their squad for all three areas from attacking front-line to midfield and defensive areas. They must prioritize to buy strong central defenders and defensive midfielders that would be basement for their success in Champions League.