And i had to make a new post due to the editing error, sad it can't be fixed as of now.
I finished the game too a bit ago and wow, out of all 3 in the main series this is the one i liked the most.
As for what i think of the ending.
Tsumugi was lying from the start about cospox, so that she could pull all that fictional character act at the end and ofc not be a suspect on Rantaro's trial.
She said also that it was the power of her ultimate talent to manage to do that kind of cosplay.
If anything never happened i don't think people with ultimate talents would exist in the first place.
In the end before being killed by Keebo she even mentioned that she failed in her Copy.
What would she copy?
I think dr1 and dr2 happened for real and after the situation calmed down and the world returned back to normal, team danganrompa got ahold of the footage from both of them and presented the killing games as a TV show.
It made a huge success with the public so much that they had to find a way to continue it and they did.
It's impossible that people who were alive by the beginning of it still were by season 53 thus explaining why there are no remnants of despair/future foundation.
This, atleast, is what i got from it.