Jira 9.1 shows the comments from newest to oldest by default.

The "Add Comment" button is displayed at the bottom, forcing the user to scroll all the way to the bottom if they want to add a comment.

The suggestion is that the "Add Comment" button shows up on top when displaying the comments in descending order OR  at the bottom if the user changes to ascending order.

Or give the user the option to change the location, such as by using a configuration property.