Surely changing suppliers should change the car development? I mean, if (for example) Lotus were to start using Mercedes engines after the car was designed for Renault engines, the car would need to be adjusted in order to make things fit properly, which could effect aerodynamics. Also, different tyres have different constructions, so that could effect aero balance.
I completely agree! Also, there shouldn't be domination of one manufacturer. We should have to compromise. Also a good idea would be limiting the number of best suppliers according to the level they are on.