Perez stated from the start the RBR was completely different from what he was used to drive. So he had to adapt. He repeated this explicitely on Thursday.
Whether taking the setup of your team mate is a weak point is hard to say. If he has been setting it up in the previous three races by himself just to find out he ends up with a setup similar to Max, then why waist precious time? It could also be useful to benchmark his driving to Max. To know the differences may help him find out where it is setup and where it is driving style/capabilities.
The story about RB suddingly being outpaced by Mercedes is not strange.
It was very clear that Mercedes was hindered by the 'diva-like' rear end of the W12. They lost speed in the corners, also in high speed corners exits. Lower corner exit speeds meant they needed to be more agressive on the battery to keep up on the straights. In Bahrein Lewis was about as quick on the straights as Max (both were midfield) but in all other sections Lewis was a bit slower.
They fixed that diva. Chapeau! So Mercedes does not lose that much or any at all on RB in the corners. And with higher corner exit speeds they can achieve higher max speeds on the straights. Portimao was a very good example. They were soo much better in Galp (last corner). No need for an agressive use of the battery. They can now stretch the deployment all the way to the end of the straights.
This is why Max said RB now lose it on deployment (which was the opposite in Bahrein). Which is a bit unfair to Honda. He is not driving an engine. He is driving a car. Red Bull needs to work on drag and grip. Like Mercedes worked on the rear end of their car.