Is that a correct line of thinking?
Sounds right. Just for further information, if you're approaching the wattage limit it's usually better to switch to a higher CDR even if you have to sacrifice some capacity (mAh). For example, if you were vaping with that setup at 75 - 80 watts, the Samsung 25R at 2,500 mAh might actually last longer on a charge than the 30Q with 3,000 mAh. This is only an issue near the limits, so with MTL vaping at lower wattages you're right that the 30Q will last longer. I guess a good rule of thumb for battery issues is to leave yourself a generous margin of error.