I have no issues with backing up but some cars do require more press on the pedal like our 2008 S550 which was a deadweight and did not have much idle speed at all without pressing the pedal. To the OP, you will get a feel for it over a few months.
My SC430 and IS300 both had an ECU that adapted to how I drove, which mostly meant that the car adapted to how I touched both pedals. I'm assuming the GS has the same technology as my older cars. If you think it's too sensitive, the car will eventually notice you touching the gas then pulling your foot off and then touching it again. It will then lower its response until you always smoothly touch it.
If the car didn't respond enough, it would notice that when you push on the gas for a moment you then push harder, and eventually it'll respond more aggressively to applying pressure. It will reach an equilibrium at which point when you add gas it'll accelerate at the amount you like without the need to push harder and harder, or needing to jerk your foot off the gas because it gave you too much.
The long and short is, the car is just too sensitive for you, but over time it will restrict it's actions to match your driving style.
I'm coming off a 2000 Audi A4 with a 5-speed so I definitely feel like the accelerator in my GS is touchy. Mostly I have trouble when parking in my garage; I have to drive slowly to make sure I don't hit anything (I have to pull in the side view mirror to get the car in). When the front wheels hi the lip of the concrete floor, I have to give it a little gas, and half the time it turns out to be too much gas.
That having been said, when exiting the garage I don't have to hit the accelerator at all, the engine idle speed moves the car just fine.
So perhaps it depends more on your previous vehicle and less on your comfort.
My GS has a huge dead spot in the pedal at first. It was really hard to get use to and always took me a long time to start going. My wife also noticed it and has an issue with it every time she drives it. And this is in normal mode not Eco. Weird.