Only in the same way that the pixels displayed in a browser are not a tree structure that you can diff - the diffing happens at a higher level of abstraction than what's rendered.

Diffing and only updating the parts of the TUI which have changed does make sense if you consider the alternative is to rewrite the entire screen every "frame". There are other ways to abstract this, e.g. a library like tqmd for python may well have a significantly more simple abstraction than a tree for storing what it's going to update next for the progress bar widget than claude, but it also provides a much more simple interface.

To me it seems more fair game to attack it for being written in JS than for using a particular "rendering" technique to minimise updates sent to the terminal.