I understand what you're saying and it is very logical. This is why I feel the system should take one to the last unread post, per thread. Using your two examples, if one is engaged in an active 'chat' with someone, the last unread post would be the latest (or one of the latest).
But if one goes to a thread they have never been to before it would take them to he oldest (first) post.
Note that the system does have a database that keeps a user profile history (since there is the 'view new thread' feature), so the above change wouldn't be that difficult to program.
This change is something I have been pushing for since the re-launching of this forum last year.
Maybe I'm misunderstanding you, but the forum does indeed have such a system. If you want to go straight to the last unread post, all you have to do is click on the circle (or star if you've posted in the topic) to the left of the topic's title.