This is correct for the track mode, because on track you either slowing down or accelerating, so the mapping is steep, up to 80% of the throttle you get almost no power at all and above that is 100%. Sport mode is what you are looking for.
Sad to hear you're not happy with the purchase.
I have 18000 km on mine (did it in 9 months) and I love it. Sure you pay M2 price for it, especially here in Europe, but BMWs are everywhere, Mustangs aren't, and DH is ever more unique. I guess they sold less than 20 DHs here in Poland so it makes it very unique. V8 plus manual is awesome...