I'm trying to modify the drops from Compressed Gravel and Compressed Dust. I assumed that the count variable was the one determining how many of that item that dropped.

The following configuration:

{  
    "name":"excompressum:compressed_block",
    "metadata":"*",
    "type":"list",
    "rewards":[  
        {  
            "name": "minecraft:dye",
            "metadata": 15,
            "count": 1,
            "chance": 0.20,
            "luck": 0.0,
            "meshLevel": 1
        }
    ]
}

Gives:

However, changing "count" to ex. 7 changes it to this:

Shouldn't *1x be the one changing to *7x and if not, how do one change that value? I'm trying to mimic the original drops, just changing which items that drops (example below).

Also, what does luck do? I changed it with no visual difference (according to JEI).

Also, if possible, a command to dump all current hammer/sieve recipes as JSON would be extremely helpful in understanding how to write your own drop-table as I had no idea meshLevel was a value since it didn't exist in the example file.

The count parameter was working as expected (it controls the item count for a drop, not the amount of rolls). But for that purpose, I've added a new "rolls" parameter for rewards that makes what you're trying to do possible without having to duplicate the entry.

Luck is a leftover from earlier versions of Ex Nihilo and is currently not in use. I've removed it from the example file and instead added the newer meshLevel parameter to it.