To me, these two Reply buttons have different meaning. The Reply on the upper right implies that I will reply to that post, whereas the Reply button at the bottom implies that I will reply to the OP.
If there is consensus, could this behavior be changed?
Changed to what exactly?
Reply to the post is intended as a direct reply to that post, usually when there are other responses in-between.
Reply to topic is intended to responses to the conversation itself, not necessarily the OP, since a discussion can develop and drift from the original post.
In practice it is useful to distinguish drifts when staff want to split a specific discussion within a topic that would better be addressed in its own topic, i.e., to keep the original intent of the OP. An example would be a topic on a specific issue deriving to an accessory concern: staff can select “post + replies” as a shortcut, and move this discussion elsewhere.
This avoids the dilution phenomenon that is often found in classical forums where a single topic covers other topics as well, leading to search engine pollution – where unrelated topics pop up in your search results that are not actionable. Discourse makes it easy to keep discussion on track and provide a much higher quality of contents.