The best pre-Zariel weapons in mod 19 are hidden behind maps that drop with a fairly low probability and the maps themselves have a very low probability of dropping the weapons.
Weapons are very game critical and easily the most sought after items.
The problem with hiding them behind a low random chance is that the spread in the number of rolls will be very large, so some players will never get the weapons even after a very large number of rolls.
Without going into probability distributions and all the complex probability theory, lets just ask: After 1000 rolls, how big percentage of your customers will not get the weapons after 1000 rolls when the expected average is 500?
Expected average 500 means roughly 0.002 drop probability(yes, I know this probably is no entirely correct, but close enough)
The probability of NOT getting anything after 1000 drops is then (1-0.002)**1000 = 0.135. 13.5% of the customers will never get the drop after rolling twice as many rolls as the expected average.
The probability of NOT getting anything after 2000 drops is then (1-0.002)**1000 = 0.018. 1.8% of the customers will never get the drop after rolling four times as many rolls as the expected average, which basically means they will never get it. If this is a very critical item you can probably expect those customers to go away.
To counter this you can use two strategies:
* Either implement a cutoff so you get a guaranteed drop after for instance(in this example) 1000 rolls. This is what you did for preservation wards.
* Use high drop probabilities, but require many drops to get the desired items. That basically means using a currency drop. With a high droprate like 0.5 the deviation in the number of required rolls will be so small that it is negligable. ( 1-0.5)**10 = 0.001, ( 1-0.5)**20 = 0,000001, and this will even even more out as you require multiple such currency drops as nobody will go to needing 20 drops several times.