Plandex isn't really focused on understanding a whole codebase. It can be used for that to some extent, but it's more designed for building larger features where you'd load in maybe 5-20 relevant files and then have Plandex build the whole feature across potentially dozens of steps and model calls. With Aider (or ChatGPT) it would require a lot more back-and-forth and user interaction to get a similar result.

Like I said, I think Aider's use of tree-sitter is a great concept and something I'd like to incorporate in some way. I'm not at all trying to claim that Plandex is 'better' than Aider for every use case. I think they are suited to different kinds of tasks.