Clay containers need to be buffed!
There are reasons:
1. You need to fire them in kiln - a hard process
2. It gives less space than new, easer crafted containers
Please buff them somehow, for example let them be unique container:
1. Can be used as container with slots
2. Can be used for liquids
Or also can be used as stockpile-kind container. For example you can hold up 60 any meat in urn.