so your point is:better having constant and known errors but repeatability as you may (or may not )have the testing environment under control?
To me real world conditions include cross winds and inconsistencies.and eliminating these in your evaluations will yield unrealistic results only repeatable in a wind tunnel or in your cfd world....
True it´s ALOT of additional work to plan your car carrying all the mounting points for measuring equipment but in the end it is the only way to gain true real world data and open the door for deeper insight what those variables as cross winds changing track temps etc are doing to your aero...It´s a lot of data to sample and analyse but sure the team that does it first will carry a huge advantage very soon given they have the capacity to make use of it all..
I rather think all that 50/60%tunnel work is creating a lot of extra work you could more efficiently use creating a 100%windtunnel model -think about it -you´d have real aero data without having to adjust scaling factors reynolds and whatever and even moreso-you can test the real mckoy -halving your output in terms of molds -as every development step has to be realised in scale + in full scale ....yes you need even bigger working areas in the tunnel with all its implications but the reward is quite high methinks.Of course it´s not allowed these days...So it´s not feasible for F1..