Seems to me...
With the same battery size, the Model 3 will accrue more miles per minute of charge than the Model S or X because it is very likely that the Model 3 will go somewhat further on the same amount of energy by being a little lighter. That assumes, though, that the Model 3 will offer the same battery size as the S. I don't think we know that yet.
If the S or X has a larger battery, the charging will probably still favor the Model 3 for weight reasons for a while, but, as the smaller Model 3 battery approaches "full," it charges more slowly, while the larger battery of the Model S or X will still be at a lower overall charge and not resist charging as much and as soon. At some point, larger battery of the S or X will surpass the power taken on by the smaller Model 3 battery, and overcome the weight advantage of the 3. This conclusion seems safe to me as Musk has already announced that the range of the Model 3 will be lower than the Model S.