Merc allows Aston to buy time in the Merc wind tunnel but it is heavily governed by the FIA. After Ferrari and Haas played the game with aerodynamicists swapping teams, having coffee breaks together, having their wind tunnel model on show, when Haas joined F1 to increase competitiveness of both teams, the rules were changed make it practically impossible to cheat in that area.
Merc aerodynamicists will not have seen the Aston model and vice versa. The FIA is monitoring this very closely and if it were possible to do this, somehow getting round the FIA, then at some point someone who knew would leave the team in a bad way and tell the FIA what was going on. McLaren's $100 million fine for looking at data for the Ferrari, many years ago, means that it would be stupid to even consider taking the risk.
The wind tunnel itself is just a tool and will not drive a solution in a particular direction (if this is what you meant) other than complicated areas like moving belt roughness which might make you run your car lower. The Merc solution has been to run the car with the rear as low as possible for years (very successfully) and it was expected with the change to ground effect, that this would continue to work very well. But it hasn't yet and the RBR approach of a car with a good amount of rake and some tricks to run very low at higher speeds, is currently the better approach.
And yes it is the arrogance of the aero development team.
Lewis can tell them what he feels is wrong, but he cannot fix it, and it is of course a big engineering problem to align the aero flow field with giving the drivers the car that they want.