The amount of blowback you experience will entirely depend on the can that you use.
The same it has been for every iteration of the MCX, as well as the AR-15.
The MCX does not have a dedicated suppressed setting, on the gas block. If you want lower back pressure/blowback, use a more flow through style can or one known for less back pressure.
I use a SIG SRD762Ti-QD on my 5.5" Rattler and don't have anything serious for blowback.
Had a Surefire SOCOM (original) on a 11.5" Spear-LT, had about the same amount of blowback as a Geissele Super Duty 11.5.