well the problem is knowing exactly what those people are doing, what kind of power draw, what kind of set upm and even what kind of battery.
If your trying to go ultra low resistance you need one of the stronger
batteries, problem is the Mah on the real powerful batteries is not very high.
then you have the other side of the coin.
the mechanical has no regulation, nothing to keep the same voltage. a fresh battery will only be at 4.2 volts for a short time before falling into the 3.7v range it is designed to run in, so higher resistance doesnt work for very long either. the battery is still ok but it is hard to really power a 2+ ohm device correctly as the battery voltage keeps falling below 4v
it is best to try to find or stay around 1.5 or lower for best performance VS battery life. this is why so many people use mechanicals with rebuildable atty's, say for example you set up a dripper at 1 ohm then get a 2600mah battery you should very easily get a full day of normal
vaping before you notice the battery getting weak. using a rebuildable lets you tune the device for best results, but low resistance prebuilt stuff works ok too.
I have a dripper set to .8 ohms on a mechanical with a 2900mah battery and i get around a day and a half if not longer before i notice the battery get weak. how hard you vape will also affect this.