Are there really no plugins for that? In Doom Emacs "cia" deletes an argument normally, which I assume is done by an evil mode plugin, so I thought there was one for Vim as well.
I'm actually kind of excited about tree-sitter - it's not a neovim feature, it's an independent project that can be used a lot of places. I think the effect will be similar to how LSP changed the landscape from "every editor does some parts of handling language X well, but the parts each editor does are different from each other" to "all the editors get this feature when the language server does", just for syntax highlighting and syntax aware edition.
Treesitter builds the AST, making it easier to create robust text objects. And it provides a unified interface for a bunch of different languages, meaning that I don't need to have 10 different plugins, one for each language, just to get access to text objects.