700 mAh for a 16340 sized cell is not that bad i think. I'm sure there are vendors that claim much higher numbers, but it's not that realistic.
The actual size for the cell in a 16340 cell is about 1/3rd of that in a 18650 (if you account for room taken up by the cell wall, spacers/isolators/contacts etc).
And surely you have 18650 cells with more that 3x700=2100 mAh capacities, but sometimes that comes with a trade-off: the capacity is larger, but the maximum discharge rate is lower. Usually the capacity of a battery is specified at 1C discharge rate, i.e. the amount of power in can supply when discharged in 1 hour.
This isn't always realistic though: in things like laptop computers and smartphones the discharge rate is much lower as those typically last several hours to a day or two on a fully charged battery. For such applications higher capacity but lower current handing cells are preferable.