For that case, you could manage a link in the first post that takes the user straight to the latest post.
P.S.: Of course, users can easily achieve this using End key or the slider, but this obviously requires that the user is familiar with keyboard shortcuts or Discourse.
Update
Actually, there is always a link to the latest reply below the first post (even if it’s hard to miss, especially but not only for new users, given that it is next to all the other information):
