Questioning Equal Performances

Hello everyone,

I have a question regarding cars with equal performance:

Whenever I start a grand prix with qualifying rounds, using cars with equal performance, it's always the top teams that end up in the front positions, while the backmarker teams finish at the bottom (both in qualifying and the race - I have tested this on multiple circuits). Is this phenomenon related to the car chassis? Since the chassis are not identical and some chassis are much better than others (especially RB), does it mean that equal performance is not truly equal?

I apologize if the question may seem silly, but I'm trying to understand.

Thank you