Yes, pre-loading is how I use the perk 90% of the time. And yes, better to empty all the chambers into your target (which is why we should be able to trigger the perk when the chambers are empty).
But I disagree it’s not useful to be able to reload before the chambers are empty. If I’m shooting at a fast mobile target, I’m typically being a bit more careful with my shots, and it’s not uncommon for a target to get behind cover before I can empty the chambers (or dies before I finish shooting all my bullets). In those cases, being able to quickly reload is very handy.
But yeah, now that I think about it more, reloading before the chambers are empty is actually more useful with Emily and Nagual.