1, using different media and carriers;
2. Brush calligraphy is more complicated and difficult than hard pen calligraphy.
3. History is different. Brush calligraphy has a history of 1000 years, while hard pen was used in Oracle Bone Inscriptions period (let's call it hard pen) and modern times.
As for the quality of calligraphy, it is the result of aesthetic differences. I will share with you what I have collected about calligraphy appreciation. Please see/wujianjunty/blog/item/697652a79a03f295d14358e6.html.