Eddie Irvine did say that Schumi couldn’t always set the car up, but would just drive around it.. put that comment with the one by Rubens about how he should have won some of MSc’s titles and we can assume that Schumi purely just outdrove him on some of his setups.. but there were periods where Rubens was very competitive/faster even, so maybe that was when he kept the setups to himself! I do seem to remember hearing that Alonso stopped sharing setups with Hamilton in 2007? Probably the same thing was happening there too..
On development drivers.. I guess it’s worth noting who is employed to do that job, i.e. being paid. De la Rosa racing for transitioning Sauber, Panis, Wurz etc. racing again.. I always had a suspicion that Davidson was also behind some great cars, the 2004 BAR, the Super Aguri that started beating the works Honda, and then of course the 2009 Brawn (but it looks like Ross credits Rubens), which was said to first be the 2009 Super Aguri..
There are also a few sim drivers such as Rossiter, Yelloly at Force India that you wouldn’t think of at first, so they must have the skills to develop the car/test it on the sim and correlate that with real world data no problem, maybe Wolff as well. Vandoorne is a very good simracer, so I wouldn’t be surprised if he was doing that for McLaren (although they’ve been nowhere for 3 seasons now, heh). Stanaway won the iRacing Pro Series when recovering from injury, so he could also have done that for Lotus when Gravity had their youngsters as the reserve drivers.