This is a fairly standard deal for first-time offenders, per other practising lawyers on YT. They suspend the prosecution before they 'officially' enter a record of his guilt, and as long as he follows the deals provisions, they never make it part of the record and it simply expires. He is not guilty until they officially find him so and make it part of the record.
In more graphic terms, they made the agreement for Nick to basically hand them a loaded gun hold it to his head until they are satisfied that he has done his part.
How much better could it really have gotten? They drop misdemeanours and a grade off the top charge.
I think I heard Nate or Kurt say that 2nd degree possession was not eligible for diversion, but I am not sure. It does not sound like much of a win unless the State had to be browbeaten into letting the women get off? I would speculate that the only real improvement would have been letting the women go if Nick took responsibility and he dithered for months about actually doing that to get the basic deal they offer everyone. This is just speculation, but I would believe Nick would make the routine process a pain and half.