I understand that they are the slowest cars on the grid, but their top speed is not limited by their drag profile but their gear ratios instead. For those who play career mode, all the drag upgrades will have no effect on increasing the top speed for these cars, due to the fact these three cars have a limited top speed due to the gear ratio. The mclaren is also Mercedes powered but is able to reach 360kph (9kph more than all other Mercedes powered cars) without hitting its gear ratio which is why I believe this to be a mistake on the other three mercedes powered cars.
Mercedes has the slowest top speed as a function of their higher final gear ratio; mclaren make their own gearbox with a lower final gear ratio giving them a higher top speed.
This is a real world representation; it would be good if Codemasters included an option to build your own gearbox like we can with the durability and power upgrades.
