Not sure where you are finding that bossk has a reduced drop rate (my personal experience hasn’t found it to be so, and I only have 6 shards remaining on him, perhaps it is an outdated site that hasn’t updated the number of attempts per day?); it is generally accepted that EVERY hard and cantina node shard farm has a drop rate of 30- 33% given a sufficient sample size.
Hard nodes are in a miles better place right now than ever before. Eight attempts per day (which if you monitor, should be netting you 2.4-2.6 shards a day) and 25 crystal refeshes is amazing; when the game launched (and for a long time after) it was 3 attempts per day, and 50 crystals for a refresh, so farming a character up free from an early release actually could take the better part of year.