I think the "deadzone" is introduced on purpose to prevent the wheel oscilations on straights.
FFB API is pretty simple and at the same time it it pretty bad, you can read more here:
Why Force Feedback In Computer Simulators Does Not Work
The faster and stronger wheel, the harder to prevent oscilations because you don't have a command in FFB API like "move to position x", you can only set the direction and force, then you have to read the position and correct the result - the faster the wheel, the more probability that you will go past the desired position. Introducing the "deadzone" you make wheel artificially slower near the desired positions.
This is how the WheelCheck works - there is no possibility for any quirks. Just read the current wheel position, set the force and after a given time read the result position.
As for the feeling difference between G27 and Thrustmaster wheels - G27 doesn't start moving at all until 16-18% given force while Thrustmaster wheels start moving at 4% force although up to the 14% the response is very small - this is the reason, next to the lack of mechanical deadzone, that the wheels feel much more responsive than G27, but to achieve the linear response at the beginning you should give the comparable min force on both wheels.
Blkout, have you tested iRacing with different wheel forces and minimum FFB? You should definitely feel the huge difference on straights. Try the Spec Racer Ford on bumpy tracks like Lime Rock, Summit Point.