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More XM-L T6s would mean higher efficiency, to a certain point, depending on the actual lumens output. Higher efficiency = higher lumens for the same watts, less heat output, which itself leads to even higher efficiency albeit that’s a slight effect only….and also longer run times which is usually more crucial in bike lights vs our flashaholic’s fun use unless if you are talking about the typical 20-30 mins ride around the neighbourhood.
You already mentioned that you’d need 2hrs, so that’s not low. Personally if you want a reasonably bright light, i’d go for the 3 or 5 x XM-L versions rather than a single XM-L. 4 x 18650 pack is what you’d wanna aim for. No need to do those 16 x XM-Ls.
There are lights utilizing more efficient emitters, but the lights do cost more also due to the “current tech” thingy.

However, more emitters without a bigger reflector (head diameter) comes at the expense of throw, coz each emitter is driven at a lower level, eg if your driver total output is say 7A total. ie lower emitter surface luminosity.

In short, it really depends on how much the driver is pushing out to the LEDs. Just take that each XM-L is capable of around 900 lumens,

You can check out the Fenix BC35R, it has a beam cutoff for the top part of the light’s output so that it does not blind oncoming traffic and pedestrains. If it’s for mountain trails riding, then typical round reflectors are fine.