P-MOSFET Gate Directly to Ground
Should be fine. The only consideration would be Vgs(max). The Darlington array would always drop some voltage across it, whatever its Vce(sat) is, which would lower the voltage across the gate and the source. If you pull the gate directly to ground, Vgs will be larger.

Of course, with a battery, you're unlikely to be anywhere near Vgs(max), but it's worth considering.