I can confirm that the luck stat is working (we log the percent chance on each drop roll so I can easily see that is higher/lower depending on if people have luck enabled). The amount of help it gives you is based on the type of drop and the existing drop chance.
It ranges from around a 5% - 25% improvement in the drop rate depending on how much luck you have active, but that’s multiplicative not additive – so if the drop chance is 10% normally you are increasing it to 10.5% - 12.5% for example.
On the one hand we want the luck equipment/potion to be “worth it”, on the other hand obviously we can’t break the entire drop chance and make it like +100% or something like that.
In Reborn I think we are going to be transitioning away from that type of +Luck since basically my take on it from watching the community discuss it is that the effect isn’t noticeable to make it worthwhile. And instead move more toward a system of getting an additional guaranteed roll for the week on your Shard Dungeon runs or something like that, where it doesn’t affect every roll but instead is a very noticeable, definite result that you will be able to easily gauge the worth of.