I think the tuning part is more than just the set up, but rather the fundamentals of the car (ie. when ERS kicks in, DRS, the wheelspin that before the update is too much, but post update is nonexistent)
I think they will try to tune the car so that it at least handles like a real life F1 car (ie. wheelspin if you smash the throttle like common sense tells us, but not too much like we had pre-update). I'm guessing it will be harder to drive, especially since the Mercedes is known as a diva, but I think as long as it's authentic that's all they're aiming for. And don't sell GTS' controller implementation short, it's amazing and the cars work just as well on either control scheme. As a testament to this some of the tunes I have in my car were made by tuners that use the DS4, but handle perfectly fine and just as how the tuner describes them. I think if controller players will not be happy with the new tweaks to the F1 but wheel users are, it will be another fundamental problem regarding the car itself rather than the setup it has