The schema grants are redundant, I just tested and confirmed. Due to inheritance, adding anything at catalog shows the same permission at schema. It even shows a hint on the Grant page in Unity:

Granted privileges will be inherited by applicable objects (e.g. schemas, tables) in this catalog. Learn more

GRANT USE_CATALOG ON CATALOG dev to `user@userdomain.com`;

GRANT USE_SCHEMA ON CATALOG dev to ``user@userdomain.com`; 

GRANT SELECT ON CATALOG dev to ``user@userdomain.com`;

Catalog

Schema