Even with their lesser energy capacity, NiMH batteries satisfy my needs and are my preference for smaller lights (where I use lower more than higher brightness levels) since I do not need to be careful with them as I would with Li-ion.
(2000 mAh Eneloop NiMH AA / 1000 mAh per Ah) x 1.2 V nominal = 2.40 Wh
(900 mAh Wurkkos Li-ion 14500 / 1000 mAh per Ah) x 3.7 V nominal = 3.33 Wh
(3.33 Li-ion Wh - 2.40 NiMH Wh) / 2.40 NiMH Wh = 0.3875
0.3875 x 100% = 38.75% more Wh Capacity from Li-ion than from NiMH