I've done about 10 stash/supply, 5-6 cache, 4 hoard and 1 trove, and gotten 1 soulbinder to legendary.
This is compared to a net tossing event I hosted on my shard last weekend, and got at least 1 full soulbinder filled from empty with each Scalis, and in one case 3 filled up at once (possibly from my being dead the previous scalis and missing out)