The 21700 can’t match the 26650 capacity, but can deliver far and away more power. I’ve found this true in the Samsung 30T and iJoy 21700’s as compared to any 26650 I’ve tested, and there’s been quite a few.
But I for one will be using the 26650 for a long time, as well as the even larger 32650, as I have lights that do very well with these package sizes.
The MiBoxer C4-12 is a favorite charger of mine, I can’t see much use for less than 1A charge to 8 cells though so this new offering has no appeal to me.