I'm unsure whether the tech limits colour reproduction, there's people who post in this section far more qualified than me to answer that, if I recall correctly the GSYNC module limits options for tweaking though.
I think it's just down to GSYNC not being required on professional colour reproduction monitors, the techs primary use is gaming so it's a different sector of the monitor market. You likely could buy an IPS GSYNC screen and get it calibrated very close to accuracy but I'm pretty sure professional monitors have much more uniform panels and far better quality control.