Could it be, you are comparing R70 to R9050? Sorry if that is not the case.
Also you are probably refering to ZeroAir’s review of M21H and 1Lumen’s review shows about 900 lumens of sustained output (same 70.3 R9050 4000K). Don’t know whose data is more accurate.
So if we can pretend that the runtimes here are all proportional to the weight of the head of the flashlights I measure;
(only measuring weight. Using provided lumen measurements.)
M21H 88g - 600 lumens(with potting material so slightly heavier, covering exposed driver components)
The M26D isn’t nearly as large as the M3-C and if lumens sustained is proportionate to weight of head and it follows the same ratio as the others you have examples of it should sustain 720 - 820 lumens if emitters are all equalized.
I still love the M26D with FC40 1800K and 3° TIR, it’s a very unique and beautiful light.