Not sure if you have every had a Corvette up to 200 mph, but the back end gets a little loose and you get this side to side swaying.
The high downforce helps to limit this and that is why there has been talk about active aero on this car for high speed runs but it wasn't announced. Maybe Zora?
I found in the Stingray the car felt more planted with the Z51 spoiler at speeds of 225 kph and above compared to the high wing where I got more swaying.
The ZR1 will reach 350 kph, so unless your planning on going full out, your right it's an aesthetic issue for how you want your car to look as most will not
be willing to get their car anywhere near those speeds.
GM still has final high speed testing to do on the ZR1, but they will not be using the big wing to get the top speed final figures.