The XP G2 has a much higher forward voltage then the XM L2, so the standard driver probably isn’t able to deliver the voltage and thus the amps the led needs to perform well.
My Jax Z1 has a dedomed XP G2 on Noctigon, bridged spring and a LD01 driver, delivering 5A.
It’s measured at 215Kcd @ 1 meter (with Sony Konion VC5, and a tad less with good 26650 such as Keeppower 4200/Efest3500 purple).
I didn’t do this mod myself but a friend on the German TLF forum, Kenjii. 
Cheers
Nico