Honestly, even without outright cheating, a manufacturer team has so many advantages it's kind of pointless.
Imagine a scenario where a brake duct needs to be redesigned to account for some change in regulation or a performance tweak. At someone like Mercedes the conversation would probably start with ok, let's dig out all of the CFD we did for this when we designed this in 2007, let's also grab the data on the changes we made on the GP2 last year, also weren't the LeMans team doing some work on this last month? From there they would be in a much better place to identify the points where they have to concentrate their efforts without expending a minute of new CFD time.
At a small new entrant team none of this data is available to them.
Imagine a scenario where a brake duct needs to be redesigned to account for some change in regulation or a performance tweak. At someone like Mercedes the conversation would probably start with ok, let's dig out all of the CFD we did for this when we designed this in 2007, let's also grab the data on the changes we made on the GP2 last year, also weren't the LeMans team doing some work on this last month? From there they would be in a much better place to identify the points where they have to concentrate their efforts without expending a minute of new CFD time.
At a small new entrant team none of this data is available to them.