Review Based on Statistics:
Just checking the files, I notice that Manor have the same amount of Drag as the Merc originally - which while Merc are not the best Drag wise, it's actually quite a feat for Manor.
Wow, you've actually lowered chassis weight by -26kg making it as light as a Merc (Manor was originally the heaviest car), as well as giving them Williams Level of Drag Reduction (Williams have the even better drag reduction then Merc). When you consider that Manor already have a Mercedies Engine which is already questionably the best, they're suddenly have equal or better performance then all other cars around them in all areas other then downforce (they're naturally 9-12% down on that from Merc).
You've adjusted the slipstream data (i have no idea on that affect), as well as reduced a drag multiplier by 10% and force 5%. Unfortunatly, I don't entirely know what those two multiplies are multiplying - so it's hard to say just how crippled in downforce they are.
At an estimate, I would say that you've put the car in about 5-6th place at most tracks originally. They're best in chassis weight, drag and engine - and so long as they can still actually turn into a corner, are really competitive.
In addition,you've tried to alter the amount RnD effect has on both the Chassis and the Drag - however you've only changed Tier1 Drag values, which I believe are redundant anyway. But as every other car has constant upgrade values for these areas, the Manor will be the very best car in the pack once it is upgraded well.
You're right though, Low Drag Manor this really is