Suggestion for thresh souls and new ancient coin in PBE

instead of each minion having a % chance of spawning a soul/coin/manathing, why not divide minions by wave and pick a number of minions randomly from each one (equal to the expected average spawns per wave)?

For example, there are 6 minions in a wave and each has a 33% chance of dropping a soul. Instead of rolling a 1/3 chance each time, why not pick 2 completely random minions per wave (or even make it 1 melee and 1 ranged minion all the time)? (you get on average 0.33 souls per minion, 0.33*6=1.98 ~= 2)

This makes it near impossible for Thresh or a coin user from having an extreme deficit/surplus over time in gold/stats due to pure luck