Most relevant for me in his thoughts is the fact that the RB seems to be completely different in handling to the RBR:

"You’re going from one of the cars that’s most forgiving to the trickiest. And so you’re having to adapt quite a lot to two very different cars. (…) But it’s not something that feels that natural to most drivers.”

Confirms what everyone has been thinking. The car is a nightmare to drive for anyone not named Verstappen. Perez got a lot of shit over the last few years, but he was one of the only drivers to handle the car well.