I disagree with the statement that the author of the first post is more than that. You don’t really own a topic. Staff can move the post into another topic, and right at that moment, the author is nothing more than the author of the post they have written.
I think the topic wrench and the post wrench have caused confusion before. Mixing the functionality between them wouldn’t clear this confusion but make things even more complicated.
Actions that affect the topic, like closing, pinning, and topic timers, are in the topic menu. Actions that affect the post, like staff notices, post ownership, and locking edits, are in the post menu.
With the argument that the author of the currently first post also being the topic author and thus the option to change it should be in the topic menu, you could also argue that pinning shows the excerpt of the first post in the topic list or as a banner, and therefore this option should be in the post menu. And we can probably find arguments for the other options too. But I think duplicating the content of these already quite feature-rich menus won’t make it easier to find what you are looking for, and keeping topic and post actions separate seems a helpful concept.