Although the cars are deemed to be equal, they never really are. Also the cars can be vastly different on the circuit due to drivers required set up, who unlike the team have the final word on car set up.A good point and if that is the case then Bottas has to up his game in qualifying to oust Hamilton from pole.
I remember Prost doing a few laps in Mansell's car at Silverstone and being seconds off the pace, and even worse when Mansell tried it in Prost's car. The team require one critical thing from the driver, feedback., There was no one better at this than Michael Schumacher, totally dedicated to getting the best out of his car, spending days in the workshop watching and learning. Ferrari were very fortunate having him, as are Mercedes now in having Hamilton.