Currently it’s not possible to use GraphStudio as a command line tool, i.e. it does not provide an interface to enter GSQL DDL (or any other type of) statements. The command line tool is
gsql, so you probably want to use a combination of the two. You can use
gsql remotely, e.g. with TigerGraph Cloud instances, so you not have to log in to a TigerGraph server to use it.
I also think that designing a graph schema in a visual way is more intuitive, less error prone and not much more time consuming or effort intensive than doing it manually. In fact, I believe that schema design is a human creative activity (borderlining art), not something that should be done in a programmatic way (not if you want optimal design) and thus visual design supports the thought process, the realisation of a vision or inspiration much better than writing DDL statements. It was/is true for RDBMS schema design (look at the variety or ERD designer tools) and even generic software system design (many UML tools), and it is even more true for graph design as graph is inherently a lot more visual technology.
But I think your question is valid; GraphStudio could/should have a command line interface; I will check if there are plans for this.