Comparing how long batteries last you for vaping says more about the vaping than it does about the batteries or the mod. Comparing how much juice a battery will get you through is better, but says as much about the efficiency of the juice delivery device as it does about the battery and mod. The only accurate way of comparing batteries' capacities is with a constant-current load at different discharge rates.
Technologies being equal, a 700 mAH battery isn't going to last 700/2000 as long as a 2000 mAH battery at the same discharge rate because the discharge current used to establish the 700 mAH rating is much less than that used to establish the 2000 mAH rating. Higher capacity batteries handle the currents we use for vaping much better.
Regulated mods can be particularly brutal on batteries, especially smaller batteries. The weaker the battery, the increasingly harder a regulated mod works it to maintain the set coil voltage (or wattage). Battery current is higher than coil current by at least a factor of the coil voltage divided by the battery voltage. The battery is regularly deeply discharged, decreasing its cycle life, and the regulated mod must have a low-voltage cut-off to protect the battery. These are the costs of regulated coil voltage.
A mechanical mod is the opposite simply due to Ohm's Law. The weaker the battery, the less the current drawn from it, and, of course, the weaker the vape. For most of the charge life, the voltage decreases gradually, and that may go unnoticed. But at the end of the charge, the voltage (and vape) drops so suddenly, it can't help but be noticed. The user will change the battery out well above the battery's minimum voltage due to the dramatically reduced vape, and some will change it out above this point. The battery is regularly less deeply discharged and a low-voltage cut-off isn't needed.
Coming full circle, before you make a consistent coil voltage your Holy Grail, consider that you are a bigger factor in vape. How hard and how long you draw probably vary all over the place--anything but consistent. Experienced mech users subconsciously compensate for gradually declining coil voltage. None of this addresses adjustability. If this is important to you, then the mech won't do it for you. You can only change the coil resistance to vary the power.