[akho]

Usability is only objective if you use the word in a dictionary sense: "it is possible to use this editor". It is very much subjective in its usual use: how easily it can be used by a certain user to do certain things. Say, to me a text editor without Vim key bindings is not usable. To someone else, Ctrl-C / Ctrl-V bindings may be preferable. 'Usable code editor' and 'usable screenplay editor' are completely different categories, even though both are text editors.

Different approaches to extensibility can exist, all of them good in certain areas. Both Emacs and VS Code are extensible; which approach is better? You'll find different opinions.

You'll need, as a minimum, to specify a language to move "integration with favorite programming language" towards objectivity.