I thought about rating criteria based on count of assets but understood that it would be bad.

Just Imagine some beginner they can make quality assets but it will take much more time than for professionals.

Professionals have already know how to draw something quickly and  they have intuition they also have already overcome many difficulties. Many of those difficulties you need to overcome 1 time then it won't be difficult for you... But first time overcoming concrete difficult is just like spending several hours or even days... Don't forget about "X Factor (overall enjoyment)". It is absolutely up to you because it shows how much do you like the pack. The pack can be high quality maybe you even rated all other criterias with 5 stars but you don't like at all so you can rate 0 stars this criteria. It is chance to avoid unfairness... ¯\_(ツ)_/¯ I hope in the process we will find compromise rule that can allow to rate and compare (if you have any ideas create a topic in community page of the jam)