ctags just gives you locations of symbol definitions.

TreeSitter will also give you locations of symbol usages, which is obviously very useful to an AI agent. You can basically think of Treesitter as having full syntactic knowledge of the code it is looking at - like a compiler's AST.

There is also a more powerful cousin of ctags, cscope (C/C++) and Pycscope (python) that additonally gives usage locations, and more, as well as gtags that does similar, but supports more languages.